#include<bits/stdc++.h>
using namespace std;
using Int = long long;
template<typename T1,typename T2> inline void chmin(T1 &a,T2 b){if(a>b) a=b;}
template<typename T1,typename T2> inline void chmax(T1 &a,T2 b){if(a<b) a=b;}

//INSERT ABOVE HERE
signed main(){
  Int n;
  cin>>n;
  vector<Int> dp(n+1,1);
  for(Int i=2;i<=n;i++) dp[i]=dp[i-1]+dp[i-2];
  cout<<dp[n]<<endl;
  return 0;
}