text: #include<stdio.h> 
  int comb_num(int, int);
   
  int main() 
  { 
      int m, n;  
  	scanf("%d%d", &m, &n);
      printf("%d", comb_num(m, n)); 
  	return 0;
  }
  int comb_num(int m, int n)
  { 
      if ( m<n || m<1 || n<1 )     return 0; 
  	if ( n == 1 )       return m; 
  	if ( n == m )       return 1; 
  	return comb_num(m-1, n) + comb_num(m-1, n-1); 
  }