#include <stdio.h>
#include <math.h>
 
double ATAN(double x);
 
int main(){
    double a;
    a = 4*(4 * ATAN(1.0/5.0) - ATAN( 1.0 / 239.0));
    printf("%.11lf", a);
 
    return 0;
}
 
double ATAN(double x){
    double y;
    double t, s;
    int n;
 
    y = x;
    t = x;
    n = 3;
    while( 1 ){
        t = - t*x*x;
        s = t/n;
        if(fabs(s) < 0.000000000001) break;
        y = y + s;
        n++; n++;
    }
    return y;
}