#include <iostream>
using namespace std;


int main() {
    int n;
    cin>>n;
    if(n==1 || n==2){cout<<1<<endl;return 0;}
     int a =1,b=1,c;
    for(int i=3;i<=n;i++ ){
        c=a+b;
        a = b;
        b = c;
    }
    cout<<b<<endl;
}
// 64 位输出请用 printf("%lld")