母牛的故事（hdu2018）——笔记待完善

#include<stdio.h>
int main()
{
    int n;
    char d;
    int f1,f2,f3,fn;
    while(scanf("%d%c",&n,&d)!=EOF)
    {
        f1=1;
        f2=2;
        f3=3;
        if(n==0)
            break;
        if(n==1)
            printf("%d\n",f1);
        else if(n==2)
            printf("%d\n",f2);
        else if(n==3)
            printf("%d\n",f3);
        else
        {
            for(int i=4;i<=n;i++)
            {
                fn=f3+f1;
                f1=f2;
                f2=f3;
                f3=fn;
            }
            printf("%d\n",fn);
        }
            
    }
}