#include <bits/stdc++.h>
using namespace std;
const int N = 1000010, inf = 1000000007, mod = inf, D = 35;
int n, a[N], x, y, t;
char s[N];
long long z, b[D][D];
int main() {
  scanf("%d %d %d", &x, &y, &t);
  b[0][0] = 1;
  for (int i = 1; i < D; i++) {
    b[i][0] = 1;
    for (int j = 1; j <= i; j++) b[i][j] = b[i - 1][j] + b[i - 1][j - 1];
  }
  for (int i = 1; i <= x; i++)
    for (int j = 1; j <= y; j++)
      if (i >= 4 && i + j == t) z += b[x][i] * b[y][j];
  printf("%I64d", z);
  return 0;
}
