#include<iostream>
using namespace std;
long long count=0;

void resolve(int n){
    long long state_1=1;
    long long state_2=1;
    for(int i=2;i<=n;i++){
        count=(state_1+state_2);
        state_1=state_2;
        state_2=count;
    }
}
int main(){
    int n;
    cin>>n;
    resolve(n);
    cout<<count<<endl;
    return 0;
}