1：迭代

//斐波那契数的第n个数
#include<stdio.h>
//unsigned long long  Fib(n)
//{
//
//	if (1 == n || 2 == n)
//		return 1;
//	else return Fib((n - 1) + Fib((n - 2);
//
//
//}
unsigned long long  Fib(n)
{

	if (n == 1 || n == 2)
		return 1;
	else
	{
		int j = 3;
		unsigned long long answer1 = 1;
		unsigned long long answer2 = 1;

		do
		{
			unsigned long long a = answer1;
			answer1 = answer1 +answer2;
			answer2 = a;
			j++;
		} while (j <= n);
		return answer1;
	}


}
int main()
{

	int n = 0;
	while(1)
	{
		scanf_s("%d", &n);
		printf("%llu\n", Fib(n));
	}

	return 0;
}

2：递归

//斐波那契数的第n个数
#include<stdio.h>
unsigned long long  Fib(n)
{

	if (1 == n || 2 == n)
		return 1;
	else return Fib(n - 1) + Fib(n - 2);


}

//unsigned long long  Fib(n)
//{
//
//	if (n == 1 || n == 2)
//		return 1;
//	else
//	{
//		int j = 3;
//		unsigned long long answer1 = 1;
//		unsigned long long answer2 = 1;
//
//		do
//		{
//			unsigned long long a = answer1;
//			answer1 = answer1 +answer2;
//			answer2 = a;
//			j++;
//		} while (j <= n);
//		return answer1;
//	}
//
//
//}
int main()
{

	int n = 0;
	while(1)
	{
		scanf_s("%d", &n);
		printf("%llu\n", Fib(n));
	}

	return 0;
}