#include <bits/stdc++.h>
int a, b, c, ans;
int main() {
  scanf("%d %d %d", &a, &b, &c);
  while (a != 1 && b != 1 && c != 1) {
    ans += 2 * (a + b + c) - 6;
    a--;
    b--;
    c--;
  }
  if (a == 1)
    ans += b * c;
  else if (b == 1)
    ans += a * c;
  else
    ans += a * b;
  printf("%d\n", ans);
  return 0;
}
