#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define dbg puts("Viva la vida");
#define CHECK(x) cout << (#x) << " is " << (x) << endl;
#define nl puts("");
typedef map<int,int> mii;
typedef map<string,int> msi;
typedef pair<int,int> pii;
typedef pair<int,pii > tii;
typedef vector <int> VI;
typedef vector<ll> VL;
typedef set<int> SI;
#define mp make_pair
#define pb push_back
#define IN(x) scanf("%d",&x);
#define INL(x) scanf("%lld",&x);
#define OUT(x) printf("%d",x);
#define OUTL(x) printf("%lld",x);
#define SP printf(" ");
#define X first
#define Y second
#define SZ(_a) (int)_a.size()
#define ALL(_a) _a.begin(),_a.end()
#define EPS 1e-9
#define PI acos(-1.0)
#define MAX 200005
#define MOD 1000000007
#define INF (1 << 31)
int DP(int n){
int fib[n+2];
fib[1]=2;
fib[2]=2;
for(int i=3; i<=n;i++ ){
fib[i]=fib[i-1] + fib[i-2];
}
return fib[n];
}
int main(){
int n;
IN(n)
cout<<DP(n);
return 0;
}
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