#include<bits/stdc++.h>
#define ll long long int
#define repv(x,y) for(auto&x:(y))
#define rep(x,z,y) for(long long int x=(z);x<(y);x++)
#define inpv(x) repv(_elem,x)cin>>_elem;
#define allof(x) x.begin(),x.end()
using namespace std;
using pll=pair<long long int,long long int>;

int main(){
    ll N;
    cin>>N;
    vector<ll>dp(N+1,0);
    dp[0]=1;
    rep(i,0,N)
    {
        dp[i+1]+=dp[i];
        if(i+2<=N)
        dp[i+2]+=dp[i];
    }
    cout<<dp[N]<<endl;
    return 0;
}