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