爬楼梯

#include <iostream>using namespace std;int com(int m,int n){    if(m < n) return 0;if(n==0)return 1;elsereturn com(m-1,n)+com(m-1,n-1);}int main (){  int n;  while (cin>>n)  {  int sum=0;    for (int i=0;i<=n/2;i++)    {         sum+=com(n-i,i);    }  cout<<sum<<endl;  }  return 0;}