童年生活二三事

#include<stdio.h>
int main()
{
  int  n,i,a,b,sum;
  while(scanf("%d",&n),n!=0)
  {
    a=1;
    b=2;
    if(n==1)
    {
      sum=1;
    }
    if(n==2)
    {
      sum=2;
    }
    if(n>=3)
    {
      for(i=3;i<=n;i++)//斐波那契数列
      {
        sum=a+b;
        a=b;
        b=sum;
      }
    }
    printf("%d\n",sum);
  }
  
  return 0;
}