杭电OJ-2070

#include 
int main()
{
	long long i,n,a1,a2,sum;
	while(scanf("%lld",&n)&&n!=-1)
	{
		sum=0;a1=0;a2=1;
		if(n==0) sum=0;
		else if(n==1) sum=1;
		else {
			for(i=2;i<=n;i++)
			{
				sum=a1+a2;
				a1=a2;a2=sum;
			}
		}
		printf("%lld\n",sum);	
	}
	return 0;
}