#include <stdio.h>
#include <stdlib.h>

int main(void) {
	
	double x, S, S1, F=0, X;
	int k=2;
	
	printf("Ââåäèòå Õ:");
	scanf("%lf", &x);
	
	X=x*x;
	S1=X/(k*k-1);
	
	do{
		S=S1;
		F+=S;
		k++;  X*=x; 
		S1=X/(k*k-1);
	}
	while(fabs(S1-S)>0.00005);
	
	printf("%lf", F);
	
	return 0;
}