#include<stdio.h>
int main()
{
	int i,n;
	float sum=0;
	
	printf("请输入所需要前n项和: ");
	scanf("%d",&n);
	n=2*n;
	for(i=2;i<=n;i+=2)
	{
		sum=sum+1.0/i;
	}
	printf("前%d项和为:%f\n",n/2,sum);
	return 0;
}