One book 1078: sum of fractional sequences

【 Title Description 】

There's a sequence of fractions  q1/p1,q2/p2,q3/p3,q4/p4,q5/p5,...., among qi+1=qi+pi, pi+1=qi,p1=1,q1=2. For example, before this sequence 6 The items are 2/1,3/2,5/3,8/5,13/8,21/13. Find the first... Of this sequence of fractions n Sum of items .

【 Input 】

Input has one line , Contains a positive integer n(n≤30).

【 Output 】

The output has a line , Contains a floating-point number , Indicates the number before the score sequence nn Sum of items , Accurate to the decimal point

4 position .

【 sample input 】

2

【 sample output 】

3.5000

#include<stdio.h>
int main()
{
	int n;
	scanf("%d", &n);
	int dp[100];
	dp[1] = 1;
	dp[2] = 2;
	int i;
	for (i = 3; i <= n + 1; i++)
	{
		dp[i] = dp[i - 1] + dp[i - 2];
	}
	double num = 0;
	for (i = 2; i <= n + 1; i++)
	{
		num += dp[i]*1.0000 / dp[i - 1];
	}
	printf("%.4f", num);
	return 0;
}