啊题解

#include<bits/stdc++.h>
using namespace std;
int main(){
int n;
cin >> n;
long long a[70] = {};
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;
}