#include<bits/stdc++.h>
using namespace std;
int main(){
    int n;cin>> n;
    long long dp[n+1];
    memset(dp,0,sizeof(dp));
    dp[0]=1;
    for(int i=0;i<n;i++){
        if(i+1<=n){
            dp[i+1]+=dp[i];
        }
        if(i+2<=n){
            dp[i+2]+=dp[i];
        }
    }
    cout << dp[n] << endl;
}