#include<bits/stdc++.h>
using namespace std;
const int N = 1e5+10;
int n;
int h[N];

bool check(int e)
{
    for (int i = 1; i <=n; i ++ )
    {
        e = e*2-h[i];
        if(e>=1e5)return true;
        if(e<0)return false;

    }
    return true;
}

int main()
{
    cin>>n;
    for (int i = 1; i <= n; i ++ )cin>>h[i];

    int l=0,r=1e5;
    while(l<r)
    {
        int mid = (l+r)>>1;
        if(check(mid)) r = mid;
        else l = mid +1;
    }

    cout<<l;
    return 0;
}