#include <bits/stdc++.h>
using namespace std;
long long n, m, t;
long long c[35][35];
void init() {
  int i, j;
  c[0][0] = c[1][0] = c[1][1] = 1;
  for (i = 2; i <= 31; i++) {
    for (j = 0; j <= i; j++) {
      if (j == 0 || j == i) {
        c[i][j] = 1;
      } else {
        c[i][j] = c[i - 1][j] + c[i - 1][j - 1];
      }
    }
  }
}
int main() {
  setbuf(stdout, NULL);
  int i, j;
  init();
  cin >> n >> m >> t;
  long long ans = 0;
  for (i = 4; i <= n; i++) {
    int girl = t - i, boy = i;
    if (girl <= 0) break;
    if (girl > m) continue;
    ans += c[n][boy] * c[m][girl];
  }
  cout << ans << endl;
  return 0;
}
