#include <bits/stdc++.h>
using namespace std;
const double pi = acos(-1.0);
int main() {
  long long res;
  int a, b, c;
  cin >> a >> b >> c;
  cout << a + b + c - 2 + (a - 1) * (b - 1) + (a - 1) * (c - 1) +
              (c - 1) * (b - 1);
  return 0;
}
