import sys

def sqrt_3(l, r, x):
    eps = 1e-10
    while(r - l > eps):
        mid = (l + r) / 2
        if (mid ** 3 > x):
            r = mid
        else:
            l = mid
    return mid

if __name__ == '__main__':
    q = float(sys.stdin.readline())
    if q > 0:
        ret = sqrt_3(0, max(1, q), q)
    else:
        ret = -sqrt_3(0, max(1, -q), -q)
    print(f'{ret:6f}')