#include <bits/stdc++.h>
using namespace std;
int main() {
  long long int n, m, t;
  scanf("%lld%lld%lld", &n, &m, &t);
  long long int triangle[100][100];
  triangle[0][0] = triangle[1][0] = triangle[1][1] = 1;
  for (long long int i = 2; i <= 30; i++) {
    triangle[i][0] = 1;
    for (long long int j = 1; j <= i; j++) {
      triangle[i][j] = triangle[i - 1][j - 1] + triangle[i - 1][j];
    }
  }
  long long int ans = 0;
  for (long long int i = 4; i < t; i++) {
    ans = ans + (triangle[n][i] * triangle[m][t - i]);
  }
  printf("%lld\n", ans);
  return 0;
}
