爬楼梯

#include<bits/stdc++.h>
using namespace std;
long long f[35];

int main()
{
	int n;
	f[1]=1;
	f[2]=2;
	cin >> n;
	for(int i=3;i<=n;i++){
		f[i]=f[i-1]+f[i-2]; 
	}
	cout << f[n] << endl;
	return 0;
}