#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  cin >> n;
  vector<int> l(n);
  long long s = 0;
  for (int i = 0; i < n; ++i) {
    cin >> l[i];
    s += l[i];
  }
  for (int i = 0; i < n; ++i) {
    s -= l[i];
    if (l[i] >= s) {
      cout << l[i] - s + 1;
      break;
    }
    s += l[i];
  }
}
