Problem:
Score : 500 points

Problem Statement

Takahashi has a string S of length N consisting of digits from 0 through 9.

He loves the prime number P. He wants to know how many non-empty (contiguous) substrings of S - there are N \times (N + 1) / 2 of them - are divisible by P when regarded as integers written in base ten.

Here substrings starting with a 0 also count, and substrings originated from different positions in S are distinguished, even if they are equal as strings or integers.

Compute this count to help Takahashi.

Constraints

1 \leq N \leq 2 \times 10^5

S consists of digits.

|S| = N

2 \leq P \leq 10000

P is a prime number.

Input

Input is given from Standard Input in the following format:

N P
S

Output

Print the number of non-empty (contiguous) substrings of S that are divisible by P when regarded as an integer written in base ten.

Sample Input 1

4 3
3543

Sample Output 1

6

Here S = 3543. There are ten non-empty (contiguous) substrings of S:

3: divisible by 3.

35: not divisible by 3.

354: divisible by 3.

3543: divisible by 3.

5: not divisible by 3.

54: divisible by 3.

543: divisible by 3.

4: not divisible by 3.

43: not divisible by 3.

3: divisible by 3.

Six of these are divisible by 3, so print 6.

Sample Input 2

4 2
2020

Sample Output 2

10

Here S = 2020. There are ten non-empty (contiguous) substrings of S, all of which are divisible by 2, so print 10.

Note that substrings beginning with a 0 also count.

Sample Input 3

20 11
33883322005544116655

Sample Output 3

68

Solution in C# (.NET Core 3.1.201) (judge verdict: Wrong Answer)

using System;
using System.Linq;
using System.Collections.Generic;
using static System.Console;
using System.Text;
using System.IO;
using static System.Math;
using System.Numerics;

namespace AtCoder
{
    class Program
    {
        static public long[] Sarray() { return ReadLine().Split().Select(long.Parse).ToArray(); }
        static public List<long> Slist() { return ReadLine().Split().Select(long.Parse).ToList(); }
        static public (T1 a, T2 b) Slice<T1, T2>()
        {
            var t = ReadLine().Split();
            return (
            (T1)Convert.ChangeType(t[0], typeof(T1)),
            (T2)Convert.ChangeType(t[1], typeof(T2)));
        }
        static long Mod = (long)1e9 + 7;
        static void Main(string[] args)
        {
            SetOut(new StreamWriter(OpenStandardOutput()) { AutoFlush = false });
            Solve();
            Out.Flush();
            Read();
        }
        static void Solve()
        {
            (long N, long P) = Slice<long, long>();
            var S = ReadLine();
            var Sn = new long[N];
            for (var i = 0; i < N; ++i)
                Sn[i] = S[i] - '0';
            Array.Reverse(Sn);
            var ans = 0L;
            var nonZero = Sn.Where(s => s != 0).Count();
            if (P == 2)
            {
                for (var i = 0; i < N; ++i)
                {
                    if (Sn[i] != 0) --nonZero;
                    if (Sn[i] == 0)
                        ans += nonZero;
                    else if (Sn[i] % 2 == 0)
                        ans += N - i;
                }
                WriteLine(ans);
                return;
            }
            if (P == 5)
            {
                for (var i = 0; i < N; ++i)
                {
                    if (Sn[i] != 0) --nonZero;
                    if (Sn[i] == 0)
                        ans += nonZero;
                    else if (Sn[i] % 5 == 0)
                        ans += N - i;
                }
                WriteLine(ans);
                return;
            }
            var Pmods = new long[10000 + 1];
            Pmods[0] = 1;
            var _10p = 1L;
            var sum = 0L;
            for (var i = 0; i < N; ++i)
            {
                sum = (sum + _10p * Sn[i] % P) % P;
                ++Pmods[sum];
                _10p = _10p * 10 % P;
            }
            foreach (var p in Pmods)
                ans += p * (p - 1) / 2;
            WriteLine(ans);
        }
    }
}