ural 1225 Flags

#include <algorithm>
#include <map>
#include <cstring>
#include <cmath>
#include <iostream>
using namespace std;
#define lson l , m , rt << 1
#define rson m + 1 , r , rt << 1 | 1
#define LL __int64
typedef long long ll;
#define PI 3.1415926
ll dp[46];
int main()
{
     int i;
     dp[1]=2;
     dp[2]=2;
     dp[3]=4;
     for(i=4;i<=45;i++)
        dp[i]=dp[i-1]+dp[i-2];
     int n;
     while(cin>>n)
        cout<<dp[n]<<endl;
     return 0;
}