URAL1225——DP——Flags

#include<cstdio>
#include<cstring>
#include<algorithm>
using namespace std;
int main()
{
    long long dp[50];
    int n;
    while(~scanf("%d",&n)){
        dp[1] = 2;
        dp[2] = 2;
        for(int i = 3; i <= n; i++)
            dp[i] = dp[i-1] + dp[i-2];
        printf("%lld\n",dp[n]);
    }
    return 0;
}