#include <bits/stdc++.h>
#define inf (0x7f7f7f7f)
#define Max(a, b) ((a) > (b) ? (a) : (b))
#define Min(a, b) ((a) < (b) ? (a) : (b))
typedef long long ll;
using namespace std;
template <class T>
inline void read(T &x){
    int ch = 0, f = 0; x = 0;
    for(; !isdigit(ch); ch = getchar()) if(ch == '-') f = 1;
    for(; isdigit(ch); ch = getchar()) x = x * 10 + ch - 48;
    if(f) x = -x;
}
const int N = 1e5 + 5;
int n, a[N * 100];
ll sum;
bool check(int x){
    ll all = 0;
    for(int i = x; i < n; i++) all += a[i];
    ll need = 1;
    for(int i = x - 1; i >= 1; i--){
        if(a[i] >= need){
            all += a[i] - need;
        }
        else{
            need += need - a[i];
            if(need > sum) return false;
        }
    }
    return (a[0] + all >= need); 
}
int main(){
    read(n);
    for(int i = 0; i < n; i++){
        read(a[i]);
        sum += a[i];
    }
    if(sum == 1){
        int ans = 1;
        for(int i = 0; i < n; i++){
            if(a[i]) ans = max(ans, i);
        }
        printf("%d", ans);
        return 0;
    }
    int l = 0, r = 1e7, ans = 0;
    while(l <= r){
        int mid = (l + r) >> 1;
        if(!check(mid)) r = mid - 1;
        else l = mid + 1, ans = mid;
    }
    assert(ans != (int) 1e7);
    printf("%d", ans);
    return 0;
}