#include <bits/stdc++.h>
using namespace std;
int main() {
  int a, b, c;
  cin >> a >> b >> c;
  if (b > a) swap(b, a);
  if (b > c) swap(b, c);
  if (a < c) swap(a, c);
  int tmp = a + b - 1;
  int ans = (a + tmp) * b / 2;
  for (int i = 1; i < c; ++i) {
    ans += a;
    ++a;
    if (a > tmp) a = tmp;
  }
  printf("%d\n", ans);
  return 0;
}
