题解

#include <bits/stdc++.h>
using namespace std;
int main(){
    int n,sum,sum1=1,sum2=1;
    cin >> n;
    if(n==1 || n==2){
        cout << "1";
        return 0;
    }
    for(int i=1;i<=(n-2);i++){
        sum=sum1+sum2;
        sum2=sum1;
        sum1=sum;
    }
    cout << sum;
	return 0;
}