#include <bits/stdc++.h>
using namespace std;
int main() {
  short int a, b, c;
  long int sum = 0;
  cin >> a >> b >> c;
  while (a >= 1 && b >= 1 && c >= 1) {
    if (a == 1 && b == 1 && c == 1)
      sum = sum + 1;
    else if ((a == 1 && b == 1) || (b == 1 && c == 1) || (c == 1 && a == 1))
      sum = sum + (a + b + c) - 2;
    else if ((a == 1) || (b == 1) || (c == 1))
      sum = sum + a * b * c;
    else
      sum = sum + 2 * (a - 1) + 2 * (b - 1) + 2 * (c - 1);
    a = a - 1;
    b = b - 1;
    c = c - 1;
  }
  cout << sum;
  return 0;
}
