include<stdio.h>

int main()
{
double r = 0;
double a = 0;
double n = 0;
a = 3.1415926;
scanf("%lf",&r); //我发现如果输入符和类型对不上，就打印不出来
n = 4arrr/3;
printf("%.3lf", n);
return 0;
}