#include <bits/stdc++.h>
using namespace std;
int main() {
  int a = 0, b = 0, c = 0, result = 0, tmp;
  cin >> a >> b >> c;
  tmp = b * c;
  result = (a - 1) * b;
  cout << result + tmp + ((c - 1) * (a - 1));
  return 0;
}
