#include <bits/stdc++.h>
using namespace std;
int main() {
  int a, b, c;
  scanf("%d%d%d", &a, &b, &c);
  if (b < a) swap(a, b);
  printf("%d\n",
         (c + c + a - 2) * (a - 1) + (c + a - 1) * (b + a - 1 - 2 * (a - 1)));
}
