#include <bits/stdc++.h> using namespace std; #define int long long //#define uint __int128_t #define pb push_back #define fi first #define se second #define rep(i,s,n) for(int i = s;i<n;i++) #define rrep(i,s,n) for(int i = (n)-1;i>=(s);i--) #define all(v) (v).begin(),(v).end() #define chmin(a,b) a=min((a),(b)) #define chmax(a,b) a=max((a),(b)) #define endl '\n' #define IOS() ios_base::sync_with_stdio(0);cin.tie(0) typedef long long ll; typedef pair<int,int>pint; typedef vector<int>vint; typedef vector<vint> vvint; typedef vector<pint>vpint; typedef pair<pint,int> P1; typedef pair<int,pint> P2; typedef pair<pint,pint> PP; const ll MOD=1000000007; const ll INF=1e18; int dp[60]; signed main() { IOS(); //(1ll<<N)シフト演算のオーバーフローに気をつける //MOD同士の引き算に注意 //cout<<fixed<<setprecision(12); int N; cin>>N; dp[0]=1; rep(i,0,N){ dp[i+1]+=dp[i]; dp[i+2]+=dp[i]; } cout<<dp[N]<<endl; return 0; }