Zzuli:1042 sum of sequence 3

Title Description

seek 1-2/3+3/5-4/7+5/9-6/11+... Before n Xiang He , The result is reserved 3 Decimal place .

Input

Enter a positive integer n(n>0).

Output

Output a real number , Retain 3 Decimal place , Take a line alone .

The sample input  Copy

5

Sample output  Copy

0.917

#include <stdio.h>
int main()
{
	int n,i,sign=1;
	double t,sum=1,term,den=3,mol=2;
	scanf("%d",&n);
	for(i=1;i<n;i++)
	{
		t=mol/den;
		sign=(-1)*sign;
		term=sign*t;
		sum=sum+term;
		den=den+2;
		mol=mol+1;
	}
	printf("%.3lf",sum);
	return 0;
}