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#include <cstdio>
#include <map>

int main() {
    int n, tmp;
    std::map<int, long long> A;
    std::scanf("%d", &n);
    for(int i = 0; i < n; i++) {
        std::scanf("%d", &tmp);
        std::map<int, long long>::iterator it = A.find(tmp);
        if(it != A.end())
            it->second += 1;
        else
            A[tmp] = 1;
    }
    for(std::map<int, long long>::iterator it = A.begin(); it != A.end(); it++) {
        if(it->second > 1) {
            std::map<int, long long>::iterator push_to = A.find(it->first + 1);
            if(push_to == A.end())
                A[it->first + 1] = it->second / 2;
            else
                push_to->second += it->second / 2;
        }
    }
    std::map<int, long long>::iterator last = A.end();
    last--;
    std::printf("%d\n", last->first);
    return 0;
}