#include<iostream>
#include<stdio.h>

using namespace std;

int main(){

    int n;
    cin>> n;

    long long fib[51];
    fib[0]=1;
    fib[1]=1;
    fib[2]=2;
    for(int i=0; i<49; i++){
        fib[i+2] = fib[i+1] + fib[i];
    }

    cout<< fib[n]<< endl;

    return 0;
}