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#include <bits/stdc++.h>
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using namespace std;
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const int N = 1e5 + 100;
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int n, a[N], ans = 1e9 + 10;
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priority_queue<int> us[2];
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struct Node {
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    int v, num;
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    friend bool operator<(const Node a, const Node b) { return a.v < b.v; }
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} d[N];
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void clear(int idx) {
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    while (!us[idx].empty()) {
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        ans = min(ans, -us[idx].top());
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        us[idx].pop();
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    }
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}
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signed main() {
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    cin >> n;
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    int cnt = 0;
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    for (int i = 1; i <= n; i++) {
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        cin >> a[i];
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    }
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    sort(a + 1, a + n + 1);
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    for (int i = 1; i <= n; i++) {
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        if (a[i] == a[i - 1]) {
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            d[cnt].num++;
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        } else {
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            d[++cnt].v = a[i];
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            d[cnt].num = 1;
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        }
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    }
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    for (int i = 1; i <= cnt; i++) {
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        int now = i & 1, pre = (i - 1) & 1;
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        if (d[i].v != d[i - 1].v + 1) {
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            clear(pre);
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        }
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        for (int j = 1; j <= d[i].num; j++) {
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            if (us[pre].empty()) {
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                us[now].push(-1);
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            } else {
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                int top = us[pre].top();
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                us[pre].pop();
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                us[now].push(top - 1);
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            }
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        }
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        clear(pre);
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    }
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    clear(0);
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    clear(1);
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    cout << ans;
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    return 0;
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}