#include <bits/stdc++.h>
using namespace std;
int foo(int a, int b, int c) {
  if (a == 1) return b * c;
  if (b == 1) return a * c;
  if (c == 1) return a * b;
  return 2 * a + 2 * (b - 1) + 2 * (c - 2) + foo(a - 1, b - 1, c - 1);
}
int main() {
  int a, b, c, tot;
  tot = 0;
  cin >> a >> b >> c;
  cout << foo(a, b, c) << endl;
  return 0;
}
