x_ = [0, -1, 1]
y_ = [0, 1, 1]
x = 4
####
n = len(x_)
y = 0
for i in range(0, n):
    p = 1
    for j in range(0, n):
        if i == j:
            continue
        p *= (x - x_[j]) / (x_[i] - x_[j])
    y += p * y_[i]
####
print(y)