#include <bits/stdc++.h>
const double pi = cos(-1.);
const double eps = 10e-6;
const double eps1 = 10e-10;
const int inf = 0x7fffffff;
const long long infl = 1ll << 62;
using namespace std;
int main() {
  int a, b, c;
  while (~scanf("%d%d%d", &a, &b, &c)) {
    printf("%d\n", (a + b - 1) * (a + c - 1) - a * (a - 1));
  }
  return 0;
}
