LI = lambda: list(map(int,input().split()))
MI = lambda: map(int,input().split())
yes = lambda: print("YES")
no = lambda: print("NO")
I = lambda: list(input())
J = lambda x: "".join(x)
II = lambda: int(input())
SI = lambda: input()
#---khan17---template
t = int(input())
print(3.14*t**2)