//求多项式1-1/2+1/3-1/4...+1/99-1/100

#include<stdio.h>

//求多项式1-1/2+1/3-1/4...+1/99-1/100
double sum(){
	int sign=1;//符号
	double sum=1.0, t, n=2.0;
	while(n<=100) {
		sign=-sign;
		t=sign/n;
		sum+=t;
		n++;
	}
	return sum;
}
	 

int main(){
	printf("%5.2lf",sum());
	return 0;
}