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#include <bits/stdc++.h>
using namespace std;

int n, t[210000], ans, a;

inline void fs(int &x) {
    register char c = 0;
    x = 0;
    while(c < 33) c = getchar_unlocked();
    do {
        x = (x << 1) + (x << 3) + c - '0';
        c = getchar_unlocked();
    } while(c > 33);
}

int main() {
    fs(n);
    for(int i = 1; i <= n; i++) {
        fs(a);
        t[a]++;
    }
    for(int i = 1; i <= 202000; i++) {
        t[i+1] += t[i]/2;
        if(t[i]) ans = max(ans, i);
    }
    cout << ans;
}