#include <bits/stdc++.h>
int ans;
void dfs(int a, int b, int c) {
  if (a == 1 || b == 1 || c == 1) {
    ans += a * b * c;
    return;
  }
  ans += (a + b + c - 3) * 2;
  dfs(a - 1, b - 1, c - 1);
}
int main() {
  int a, b, c;
  scanf("%d%d%d", &a, &b, &c);
  ans = 0;
  dfs(a, b, c);
  printf("%d\n", ans);
  return 0;
}
