#include <bits/stdc++.h>
using namespace std;
int a, b, c;
bool flag = true;
int func() {
  if (a > 1) {
    a--;
    b--;
    c--;
    return (a + b + c + 3) * 2 - 6;
  } else if (a == 1) {
    a--;
    if (b == 1 && c == 1) {
      flag = false;
      return 1;
    } else if (b == 1) {
      flag = false;
      return c;
    } else {
      b -= 2;
      c -= 2;
      return 2 * (b + c + 4) - 4;
    }
  } else {
    if (b == 0) {
      flag = false;
      return 0;
    } else if (b == 1) {
      flag = false;
      return c;
    } else {
      b -= 2;
      c -= 2;
      return 2 * (b + c + 4) - 4;
    }
  }
}
int main() {
  scanf("%d%d%d", &a, &b, &c);
  int sum = 0;
  int x = min(min(a, b), c);
  int z = max(max(a, b), c);
  int y = a + b + c - x - z;
  a = x;
  b = y;
  c = z;
  while (flag) {
    sum += func();
  }
  printf("%d\n", sum);
  return 0;
}
