N

#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#define PI acos(-1.)
double yy;
double f0(double x){
    return (PI - 2 * x) / (2 * sin(x) * sin(x)) - 1 / tan(x) - yy;
}
double findroot(double lb,double ub,double eps2,double(*pfunc)(double)){
    double mid,f = 1e3;
    while(fabs(f) > eps2){
        mid = (lb + ub) / 2;
        f = pfunc(mid);
        if(lb > ub){
            break;
        }
        else{
            if(f > 0){
                lb = mid;
            }
            else if(f < 0){
                ub = mid;
            }
        }
    }
    return mid;
}
int main(int argc,char **argv){
    scanf("%lf",&yy);
    printf("%.6f\n",findroot(0,5000,1e-10,f0));
    return 0;
}