#include <stdio.h>
#include <math.h>
int main(void) {
    double a ,b, d, x, x1;
    a=-2;
	b=4;
	d=0.0000000001;
	do {
		x=(a+b)/2;
		x1=(x-cos(x))*(a-cos(a));
		if (x1<0) b=x;
		else a=x;
	} while((b-a)>d);
	x=(a+b)/2;
	printf("%.10f\n",x);
}