#include <bits/stdc++.h>
using namespace std;
long long C[40][40];
int main() {
  memset(C, 0, sizeof(C));
  for (int i = 0; i < 40; i++) C[i][0] = 1;
  for (int i = 1; i < 31; i++)
    for (int j = 1; j <= i; j++) C[i][j] = C[i - 1][j] + C[i - 1][j - 1];
  int n, m, t;
  scanf("%d%d%d", &n, &m, &t);
  long long result = 0;
  for (int i = max(4, t - m); i <= min(n, t - 1); i++)
    result += C[n][i] * C[m][t - i];
  printf("%I64d", result);
  return 0;
}
