#include<stdio.h>
main()
{
    int  i;
    float sum,sign;
    i=1;
    sum=0;
    sign=1.0;
    while((1.0/i)>=1e-4)
	{
        sum += sign / i ;
        i++;
        sign = - sign;
	}
    printf("sum=%.4f",sum);
}