#include <iostream>
#include <fstream>
#define LL unsigned long long int
using namespace std;

LL N,dp[1000];

int main(){
    ifstream in("nunta.in");
    ofstream out("nunta.out");
    in >> N;

    LL i;
    dp[1]=1,dp[2]=2;
    for (i=3; i<=N; i++)
        dp[i]=dp[i-1]+dp[i-2];

    out << dp[N];
    return 0;
}