#include<bits/stdc++.h>
using namespace std;
using ll = long long;
int main() {
ll n, m, r, x, y, i, j, ans,s, lo, hi, mid, sum, t;
cin >> n;
ll a[n + 2], pre[n + 2];
pre[0] = 0;
ans = 0;
for (i = 1; i <= n; i ++) cin >> a[i], pre[i] = pre[i - 1] + a[i];
for (i = 1; i <= n; i ++) {
lo = 1;
hi = 1e18;
while (lo < hi) {
mid = (lo + hi)/2;
sum =pre[n];
s = lower_bound(pre + 1, pre + n + 1, pre[i - 1] + mid) - pre;
if ( s > n) {
hi = mid;
continue;
}
s ++;
// cout << s << "S";
r = lower_bound(pre + 1, pre + n + 1, pre[s - 1] + mid) - pre;
if ( r > n) {
hi = mid;
continue;
}
sum -= (pre[r ] - pre[i - 1]);
//cout << mid << " " << sum << " " << r << endl;
if( sum < mid) hi = mid;
else lo = mid + 1;
}
ans = max(ans, lo);
}
cout << ans - 1 << endl;
}
