Flags

1225. Flags

Time limit: 1.0 second
Memory limit: 64 MB

On the Day of the Flag of Russia a shop-owner decided to decorate the show-window of his shop with textile stripes of white, blue and red colors. He wants to satisfy the following conditions:

1. Stripes of the same color cannot be placed next to each other.
2. A blue stripe must always be placed between a white and a red or between a red and a white one.

Determine the number of the ways to fulfill his wish.

Example. For N = 3 result is following:

Input

N, the number of the stripes, 1 ≤ N ≤ 45.

Output

M, the number of the ways to decorate the shop-window.

Sample

input	output
3	4

#include <iostream>
#include<cstdio>
#include<cstring>

using namespace std;
#define maxn 50

long long dp[maxn][2];//w 0 r 1//easy
int n;

void read()
{
    scanf("%d",&n);
}

void DP()
{
    dp[1][0]=1;dp[2][0]=1;
    dp[1][1]=1;dp[2][1]=1;
    for(int i=3;i<=n;i++)
    {
        dp[i][0]=dp[i-1][1]+dp[i-2][1];
        dp[i][1]=dp[i-1][0]+dp[i-2][0];
    }
    printf("%lld\n",dp[n][0]+dp[n][1]);
}

int main()
{
    read();
    DP();
    return 0;
}