#include <bits/stdc++.h>
using namespace std;
void mohammed() {
  ios::sync_with_stdio(0);
  ios_base::sync_with_stdio(0);
  cin.tie(0), cout.tie(0);
}
int MOD = 1000000007;
int main() {
  mohammed();
  long long a, b, c;
  cin >> a >> b >> c;
  cout << (a * b + a * c + b * c) - (a + b + c) + 1;
  return 0;
}
