#include <bits/stdc++.h>
void orden(int &a, int &b) {
  if (a > b) {
    int aux = a;
    a = b;
    b = aux;
  }
}
int main() {
  int a, b, c, s1, s2;
  scanf("%d %d %d", &a, &b, &c);
  orden(a, b);
  orden(b, c);
  orden(a, b);
  s1 = (b - 1) * b / 2 + (b - 1) * (a - 1);
  s2 = (a + b - 1) * (c - b + 1);
  printf("%d\n", 2 * s1 + s2);
  return 0;
}
