S - story HDU cow --2018

S - the story of a cow  HDU - 2018 

Have a cow, it is born heifer beginning of each year. Each heifers from the fourth year, but also the beginning of a heifer born each year. Please programming in year n, when the total number of cows? 

Input

A plurality of test input data examples, each test case per line, comprising an integer n (0 <n <55) , n the meanings as described in the title. 
n = 0 indicates the end of input data, without processing.

Output

For each test case, the number of outputs of the n-th time in cows. 
Each output per line.

Sample Input

2
4
5
0

Sample Output

2
4
6

Code Example:

#include<stdio.h>
#define N 55
int main(){
    int n;
    while(~scanf("%d",&n)&&n){
        int a[N]={0};
        for(int i=0;i<n;i++){
            if(i<4) a[i]=i+1;
            else a[i]=a[i-1]+a[i-3];
        }
        printf("%d\n",a[n-1]);
    }
}

This problem will be simpler to use the number of columns, the number of columns of the usefulness of many, the future will open a special thematic point of view.