def solver(D):
    if D < 4:
        return 0
    hi = D // 4
    if D < (hi*4):
        for i in range(1,hi+1):
            lo = hi - i
            if D - (hi*2 + lo*2) < 2:
                break
    else:
        for i in range(hi+1):
            lo = hi + i
            if D - (hi*2 + lo*2) < 2:
                break
    return lo*hi

print(solver(int(input())))