Tính tổng.

//S(x,n) = -x + (x^2)/(1+2) - (x^3)/(1+2+3) + (x^4)/(1+2+3+4) + ... + (-1)n (x^n)/(1+2+3+⋯+n)
// tinh S= -x + (x^2)/(1+2) + ...+ (-1)^n * x^n/ (1+2+3+...+n)
// Khai bao cac ham thu vien neu co
#include<stdio.h>
#include<conio.h>
void main()
{
	int x,n;
	scanf("%d%d",&x,&n);
	long double T=1;
	long double S=0;
	long double tong=0;
	for(int i=1;i<=n;i++)
	{
		if(i%2!=0)
		{
			T=T*x;
			S=S+i;
			tong=tong -(long double) T/S;
		}
		else
		{
			T=T*x;
			S=S+i;
			tong=tong +(long double) T/S;
		}
	}
	printf("%.2lf",tong);// lay 2 chu so thap phan.
}