思路
$$ \begin{aligned} ans &= (x + m \times 10^k) \bmod n \\ &= [x + (m \times 10^k) \bmod n] \bmod n \\ &= [x + m \times (10^k \bmod n)] \bmod n \end{aligned} $$
n, m, k, x = [int(x) for x in input().split()]
def mpow(a, b, m):
p = 1 % m
while b:
if b & 1 == 1: p = p * a % m
a = a * a % m
b >>= 1
return p
print((x + m * mpow(10, k, n)) % n)