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;
}