#include <bits/stdc++.h>
using namespace std;
int a, b, c, maxt, circle, ans;
int main() {
  cin >> a >> b >> c;
  maxt = a + min(b, c) - 1;
  circle = b + c - 1;
  ans = (a + maxt) * (maxt - a + 1) + (circle - (maxt - a + 1) * 2) * maxt;
  cout << ans << endl;
  return 0;
};
