#include <bits/stdc++.h>
using namespace std;
int a[3];
int main() {
  int ans;
  scanf("%d %d %d", &a[0], &a[1], &a[2]);
  sort(a, a + 3);
  ans = (a[2] + a[0] - 1) * (a[1] + a[0] - 1) - (a[0] * (a[0] - 1));
  printf("%d\n", ans);
  return 0;
}
