第一轮 H

Flags
Time Limit:1000MS     Memory Limit:65536KB     64bit IO Format:%I64d & %I64u
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Description
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:

    Stripes of the same color cannot be placed next to each other.
    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:
Problem illustration

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

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

Sample Input
input	output

3

4

放第i个的时候，有两种方法：
      一、在第i 个上放上与i-1个相反的颜色（第i-1个是红色，则放白色，否则放红色）;
      二、将第i-1个的颜色改成蓝色的;
综合上述的两种情况：ans[i]=ans[i-1]+ans[i-2]
/*************************************************************************
	> File Name: h.cpp
	> Author:yuan
	> Mail:
	> Created Time: 2014年11月09日 星期日 20时41分18秒
 ************************************************************************/

#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#include<cstdlib>
#include<cmath>
using namespace std;
long long ans[50];
int n;
int main()
{
    ans[1]=ans[2]=2;ans[0]=0;
    for(int i=3;i<=45;i++)
    {
        ans[i]=ans[i-1]+ans[i-2];
    }
    while(~scanf("%d",&n)){
        printf("%I64d\n",ans[n]);
    }
    return 0;
}