#include <bits/stdc++.h>
using namespace std;
const int INF = (1 << 30) - 1;
const long double EPS = 1e-9;
const long double PI = fabs(atan2(0.0, -1.0));
void solve() {
  int a, b, c;
  cin >> a >> b >> c;
  cout << a * b * c - (a - 1) * (b - 1) * (c - 1);
}
int main() {
  solve();
  return 0;
}
