#include "bits/stdc++.h"
#define REP(i,n,N) for(ll i=(n); i<(N); i++)
#define RREP(i,n,N) for(ll i=(N-1); i>=n; i--)
#define CK(n,a,b) ((a)<=(n)&&(n)<(b))
#define ALL(v) (v).begin(),(v).end()
#define p(s) cout<<(s)<<endl
#define p2(a,b) cout<<(a)<<" "<<(b)<<endl
typedef long long ll;
using namespace std;
const ll inf=LONG_LONG_MAX;


ll N;

int main(){
    while(cin>>N){

        ll dp[55] = {};
        dp[0]=1;
        REP(i,0,N){
            dp[i+1]+=dp[i];
            dp[i+2]+=dp[i];
        }
        p(dp[N]);
    }

    return 0;
}