#include <bits/stdc++.h>
using namespace std;
int main(int argc, const char* argv[]) {
  int a[3];
  cin >> a[0] >> a[1] >> a[2];
  sort(a, a + 3);
  cout << (a[2] + a[0] - 1) * (a[1] + a[0] - 1) - (a[0] * (a[0] - 1)) << endl;
  return 0;
}
