Problem: There is an arithmetic progression with L terms: s_0, s_1, s_2, ... , s_{L-1}.  The initial term is A, and the common difference is B. That is, s_i = A + B \times i holds.  Consider the integer obtained by concatenating the terms written in base ten without leading zeros. For example, the sequence 3, 7, 11, 15, 19 would be concatenated into 37111519. What is the remainder when that integer is divided by M?

Submission attempts (in order):
class SquareMatrix():
    def __init__(self, n, mod=1000000007):
        self.n = n
        self.mat = [[0 for j in range(n)] for i in range(n)]
        self.mod = mod

    @staticmethod
    def id(n, mod=1000000007):
        res = SquareMatrix(n, mod)
        for i in range(n):
            res.mat[i][i] = 1
        return res

    @staticmethod
    def modinv(n, mod):
        assert n % mod != 0
        c0, c1 = n, mod
        a0, a1 = 1, 0
        b0, b1 = 0, 1
        while c1:
            a0, a1 = a1, a0 - c0 // c1 * a1
            b0, b1 = b1, b0 - c0 // c1 * b1
            c0, c1 = c1, c0 % c1
        return a0 % mod

    def set(self, arr):
        for i in range(self.n):
            for j in range(self.n):
                self.mat[i][j] = arr[i][j] % self.mod

    def operate(self, vec):
        assert len(vec) == self.n
        res = [0 for _ in range(self.n)]
        for i in range(self.n):
            for j in range(self.n):
                res[i] += self.mat[i][j] * vec[j]
                res[i] %= self.mod
        return res

    def add(self, other):
        assert other.n == self.n
        res = SquareMatrix(self.n, self.mod)
        for i in range(self.n):
            for j in range(self.n):
                res.mat[i][j] = self.mat[i][j] + other.mat[i][j]
                res.mat[i][j] %= self.mod
        return res

    def subtract(self, other):
        assert other.n == self.n
        res = SquareMatrix(self.n, self.mod)
        for i in range(self.n):
            for j in range(self.n):
                res.mat[i][j] = self.mat[i][j] - other.mat[i][j]
                res.mat[i][j] %= self.mod
        return res

    def times(self, k):
        res = SquareMatrix(self.n, self.mod)
        for i in range(self.n):
            for j in range(self.n):
                res.mat[i][j] = self.mat[i][j] * k
                res.mat[i][j] %= self.mod
        return res

    def multiply(self, other):
        assert self.n == other.n
        res = SquareMatrix(self.n, self.mod)
        for i in range(self.n):
            for j in range(self.n):
                for k in range(self.n):
                    res.mat[i][j] += self.mat[i][k] * other.mat[k][j]
                    res.mat[i][j] %= self.mod
        return res

    def power(self, k):
        tmp = SquareMatrix(self.n, self.mod)
        for i in range(self.n):
            for j in range(self.n):
                tmp.mat[i][j] = self.mat[i][j]
        res = SquareMatrix.id(self.n, self.mod)
        while k:
            if k & 1:
                res = res.multiply(tmp)
            tmp = tmp.multiply(tmp)
            k >>= 1
        return res

    def trace(self):
        res = 0
        for i in range(self.n):
            res += self.mat[i][i]
            res %= self.mod
        return res

    def determinant(self):
        res = 1
        tmp = SquareMatrix(self.n, self.mod)
        for i in range(self.n):
            for j in range(self.n):
                tmp.mat[i][j] = self.mat[i][j]
        for j in range(self.n):
            if tmp.mat[j][j] == 0:
                for i in range(j + 1, self.n):
                    if tmp.mat[i][j] != 0:
                        idx = i
                        break
                else:
                    return 0
                for k in range(self.n):
                    tmp.mat[j][k], tmp.mat[idx][k] = tmp.mat[idx][k], tmp.mat[j][k]
                res *= -1
            inv = SquareMatrix.modinv(tmp.mat[j][j], self.mod)
            for i in range(j + 1, self.n):
                c = -inv * tmp.mat[i][j] % self.mod
                for k in range(self.n):
                    tmp.mat[i][k] += c * tmp.mat[j][k]
                    tmp.mat[i][k] %= self.mod
        for i in range(self.n):
            res *= tmp.mat[i][i]
            res %= self.mod
        return res

    def transpose(self):
        res = SquareMatrix(self.n, self.mod)
        for i in range(self.n):
            for j in range(self.n):
                res.mat[i][j] = self.mat[j][i]
        return res

    def inverse(self): #self.determinant() != 0
        res = SquareMatrix.id(self.n, self.mod)
        tmp = SquareMatrix(self.n, self.mod)
        sgn = 1
        for i in range(self.n):
            for j in range(self.n):
                tmp.mat[i][j] = self.mat[i][j]
        for j in range(self.n):
            if tmp.mat[j][j] == 0:
                for i in range(j + 1, self.n):
                    if tmp.mat[i][j] != 0:
                        idx = i
                        break
                else:
                    return 0
                for k in range(self.n):
                    tmp.mat[j][k], tmp.mat[idx][k] = tmp.mat[idx][k], tmp.mat[j][k]
                    res.mat[j][k], res.mat[idx][k] = res.mat[idx][k], res.mat[j][k]
            inv = SquareMatrix.modinv(tmp.mat[j][j], self.mod)
            for k in range(self.n):
                tmp.mat[j][k] *= inv
                tmp.mat[j][k] %= self.mod
                res.mat[j][k] *= inv
                res.mat[j][k] %= self.mod
            for i in range(self.n):
                c = tmp.mat[i][j]
                for k in range(self.n):
                    if i == j:
                        continue
                    tmp.mat[i][k] -= tmp.mat[j][k] * c
                    tmp.mat[i][k] %= self.mod
                    res.mat[i][k] -= res.mat[j][k] * c
                    res.mat[i][k] %= self.mod
        return res

    def linear_equations(self, vec):
        return self.inverse().operate(vec)

L, A, B, M = map(int, input().split())

D = [0 for _ in range(18)]

for i in range(18):
    D[i] = int('9' * (i + 1)) - A) // B + 1
    D[i] = max(D[i], 0)
    D[i] = min(D[i], L)

for i in range(17)[::-1]:
    D[i + 1] -= D[i]

mat = SquareMatrix.id(3, M)

for i in range(18):
    op = SquareMatrix(3, M)
    op.mat[0][0] = 10**(i + 1)
    op.mat[0][1] = 1
    op.mat[1][1] = 1
    op.mat[1][2] = B
    op.mat[2][2] = 1
    mat = op.power(D[i]).multiply(mat)

print(mat.operate([0, A, 1])[0])


class SquareMatrix():
    def __init__(self, n, mod=1000000007):
        self.n = n
        self.mat = [[0 for j in range(n)] for i in range(n)]
        self.mod = mod

    @staticmethod
    def id(n, mod=1000000007):
        res = SquareMatrix(n, mod)
        for i in range(n):
            res.mat[i][i] = 1
        return res

    @staticmethod
    def modinv(n, mod):
        assert n % mod != 0
        c0, c1 = n, mod
        a0, a1 = 1, 0
        b0, b1 = 0, 1
        while c1:
            a0, a1 = a1, a0 - c0 // c1 * a1
            b0, b1 = b1, b0 - c0 // c1 * b1
            c0, c1 = c1, c0 % c1
        return a0 % mod

    def set(self, arr):
        for i in range(self.n):
            for j in range(self.n):
                self.mat[i][j] = arr[i][j] % self.mod

    def operate(self, vec):
        assert len(vec) == self.n
        res = [0 for _ in range(self.n)]
        for i in range(self.n):
            for j in range(self.n):
                res[i] += self.mat[i][j] * vec[j]
                res[i] %= self.mod
        return res

    def add(self, other):
        assert other.n == self.n
        res = SquareMatrix(self.n, self.mod)
        for i in range(self.n):
            for j in range(self.n):
                res.mat[i][j] = self.mat[i][j] + other.mat[i][j]
                res.mat[i][j] %= self.mod
        return res

    def subtract(self, other):
        assert other.n == self.n
        res = SquareMatrix(self.n, self.mod)
        for i in range(self.n):
            for j in range(self.n):
                res.mat[i][j] = self.mat[i][j] - other.mat[i][j]
                res.mat[i][j] %= self.mod
        return res

    def times(self, k):
        res = SquareMatrix(self.n, self.mod)
        for i in range(self.n):
            for j in range(self.n):
                res.mat[i][j] = self.mat[i][j] * k
                res.mat[i][j] %= self.mod
        return res

    def multiply(self, other):
        assert self.n == other.n
        res = SquareMatrix(self.n, self.mod)
        for i in range(self.n):
            for j in range(self.n):
                for k in range(self.n):
                    res.mat[i][j] += self.mat[i][k] * other.mat[k][j]
                    res.mat[i][j] %= self.mod
        return res

    def power(self, k):
        tmp = SquareMatrix(self.n, self.mod)
        for i in range(self.n):
            for j in range(self.n):
                tmp.mat[i][j] = self.mat[i][j]
        res = SquareMatrix.id(self.n, self.mod)
        while k:
            if k & 1:
                res = res.multiply(tmp)
            tmp = tmp.multiply(tmp)
            k >>= 1
        return res

    def trace(self):
        res = 0
        for i in range(self.n):
            res += self.mat[i][i]
            res %= self.mod
        return res

    def determinant(self):
        res = 1
        tmp = SquareMatrix(self.n, self.mod)
        for i in range(self.n):
            for j in range(self.n):
                tmp.mat[i][j] = self.mat[i][j]
        for j in range(self.n):
            if tmp.mat[j][j] == 0:
                for i in range(j + 1, self.n):
                    if tmp.mat[i][j] != 0:
                        idx = i
                        break
                else:
                    return 0
                for k in range(self.n):
                    tmp.mat[j][k], tmp.mat[idx][k] = tmp.mat[idx][k], tmp.mat[j][k]
                res *= -1
            inv = SquareMatrix.modinv(tmp.mat[j][j], self.mod)
            for i in range(j + 1, self.n):
                c = -inv * tmp.mat[i][j] % self.mod
                for k in range(self.n):
                    tmp.mat[i][k] += c * tmp.mat[j][k]
                    tmp.mat[i][k] %= self.mod
        for i in range(self.n):
            res *= tmp.mat[i][i]
            res %= self.mod
        return res

    def transpose(self):
        res = SquareMatrix(self.n, self.mod)
        for i in range(self.n):
            for j in range(self.n):
                res.mat[i][j] = self.mat[j][i]
        return res

    def inverse(self): #self.determinant() != 0
        res = SquareMatrix.id(self.n, self.mod)
        tmp = SquareMatrix(self.n, self.mod)
        sgn = 1
        for i in range(self.n):
            for j in range(self.n):
                tmp.mat[i][j] = self.mat[i][j]
        for j in range(self.n):
            if tmp.mat[j][j] == 0:
                for i in range(j + 1, self.n):
                    if tmp.mat[i][j] != 0:
                        idx = i
                        break
                else:
                    return 0
                for k in range(self.n):
                    tmp.mat[j][k], tmp.mat[idx][k] = tmp.mat[idx][k], tmp.mat[j][k]
                    res.mat[j][k], res.mat[idx][k] = res.mat[idx][k], res.mat[j][k]
            inv = SquareMatrix.modinv(tmp.mat[j][j], self.mod)
            for k in range(self.n):
                tmp.mat[j][k] *= inv
                tmp.mat[j][k] %= self.mod
                res.mat[j][k] *= inv
                res.mat[j][k] %= self.mod
            for i in range(self.n):
                c = tmp.mat[i][j]
                for k in range(self.n):
                    if i == j:
                        continue
                    tmp.mat[i][k] -= tmp.mat[j][k] * c
                    tmp.mat[i][k] %= self.mod
                    res.mat[i][k] -= res.mat[j][k] * c
                    res.mat[i][k] %= self.mod
        return res

    def linear_equations(self, vec):
        return self.inverse().operate(vec)

L, A, B, M = map(int, input().split())

D = [0 for _ in range(18)]

for i in range(18):
    D[i] = (int('9' * (i + 1)) - A) // B + 1
    D[i] = max(D[i], 0)
    D[i] = min(D[i], L)

for i in range(17)[::-1]:
    D[i + 1] -= D[i]

mat = SquareMatrix.id(3, M)

for i in range(18):
    op = SquareMatrix(3, M)
    op.mat[0][0] = 10**(i + 1)
    op.mat[0][1] = 1
    op.mat[1][1] = 1
    op.mat[1][2] = B
    op.mat[2][2] = 1
    mat = op.power(D[i]).multiply(mat)

print(mat.operate([0, A, 1])[0])

Verdicts: Runtime Error

Accepted