#include <bits/stdc++.h>
#include <math.h>
#define pi acos(0.0)
//#define pi 3.1416
int main()
{
double n;
while(scanf("%lf",&n) != EOF )
{
//poligon_inte_angle = (3/5)*180=(108 degree)as figure sides n=5;
//square_inte_angle = (2/4)*90=(63 degree) as figure sides n=4;
printf("%.10lf\n",( n*sin(108*pi/90 ) / sin(63*pi/90) ));//* pi/90
}
return 0;
}
0 Comments