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#include <cstdio>
#include <queue>
using namespace std;

int main() {
    int n;
    scanf("%d", &n);
    priority_queue<int> qu;
    for(int i = 0; i < n; ++i) {
        int a;
        scanf("%d", &a);
        qu.push(-a);
    }

    while(qu.size() > 1) {
        int a, b;
        a = qu.top();
        qu.pop();
        b = qu.top();
        if(a != b) {
            continue;
        }

        qu.pop();
        qu.push(a-1);
    }

    printf("%d\n", -qu.top());

    return 0;
}