递推

#include<bits/stdc++.h>
using namespace std;
int main(){
    long long a[1000],n;
    cin>>n;
    a[1] = 1;
    a[2] = 2;
    for(int i = 3;i<=n;i++){
        a[i] = a[i-1]+a[i-2];
    }
    cout<<a[n];
    return 0;
}