#include <bits/stdc++.h>
long long chooses[31][31];
using namespace std;
long long factorial(long long a) {
  long long answer = 1;
  for (long long i = 1; i <= a; i++) answer *= i;
  return answer;
}
void ch(int i, int j) {
  if (j == 0 or j == i) {
    chooses[i][j] = 1;
  } else
    chooses[i][j] = chooses[i - 1][j - 1] + chooses[i - 1][j];
}
void doChooses() {
  for (int i = 0; i < 31; i++)
    for (int j = 0; j <= i; j++) ch(i, j);
}
int main() {
  doChooses();
  long long n, m, t;
  cin >> n >> m >> t;
  long long answer = 0;
  long long temp = 0;
  temp = max(t - n, 1ll);
  for (long long girls = temp;
       (girls <= t - 4) and (girls <= m) and (t - girls <= n); girls++) {
    long long currWays = chooses[m][girls] * chooses[n][t - girls];
    answer += currWays;
  }
  cout << answer << endl;
  return 0;
}
