#include <iostream>
#include <algorithm>
#include <cstdio>
#include <string>

#define ll long long

using namespace std;

int main(){

   int n;
   cin>>n;
   ll dp[51];
   dp[0]=1,dp[1]=1;
   for(int i=2;i<=n;++i) dp[i]=dp[i-1]+dp[i-2];
   cout<<dp[n]<<endl;

   return 0;
}