text: #include <stdio.h>
  
  int ToHop(int n, int k)
  {
  	if (k == 0 || k == n)
  		return 1;
  	return (ToHop(n - 1, k - 1) + ToHop(n - 1, k));
  }
  
  int main()
  {
  	int n, k, TOHOP.OUT;
  	
  	printf("Nhap N: ");
  	scanf("%d", &n);
  	while (n<2 || (n>30));
  	{
  		printf("Nhap lai N:");
  		scanf("%d", &n);
  	}
  	printf("Nhap K: ");
  	scanf("%d", &k);
  	while(k<0 || n.k);
  	{
  		printf("Nhap lai k:");
  		scanf("%d", &k);
  	}
  	
  	TOHOP.OUT = ToHop(n, k);
  	printf("Ket Qua: %d", KetQua);
  	return 0;
  }
  