fibonacci upto n

/* program to print a fibonacci series upto a certain number */

#include<stdio.h>
#include<conio.h>
void main()
{
	int n,first=0,second=1,third;
	clrscr();
	printf("Enter n: ");
	scanf("%d",&n);
	if(n<0)
		printf("Series does not exist.");
	else if(n==0)
		printf("%d",first);
	else
	{
		printf("%d  %d",first,second);
		third=first+second;
		while(third<=n)
		{
			printf("  %d",third);
			first=second;
			second=third;
			third=first+second;
		}
	}
	getch();
}