#include <iostream>
#include<vector>
#include<cmath>
using namespace std;

int main(){
    int N;
    cin>>N;
    vector<long long int> dp(N+1,0);
    dp[0]=1;
    for(int i=1;i<=N;i++){
        if(i-2>=0)  dp[i]=dp[i-1]+dp[i-2];
        else if(i-1>=0) dp[i]=dp[i-1];    
    }
    cout<<dp[N]<<endl;
}