#include <bits/stdc++.h>
using namespace std;
 
int main()
{
    string g;
    int n, k;
    cin >> n >> k >> g;
 
    int maxi = -1;
 
    for (int i = 0; i <= n - 1; i++)
    {
        unordered_map<char, int> b; // In this map only distinct characters and distinct frequency is stored 
 
        for (int j = i; j <= n - 1; j++)
        {
            // Count the current character
            char number = g[j]; // g[j] means original input string store in number
            b[number] = b[number] + 1; // and increment it count the currrent character
 
            int l = j - i + 1;
 
            // Check exactly k distinct characters
            if (b.size() == k) // b.size will give us number key- value pairs stored in map 
            {
                maxi = max(maxi, l);
            }
        }
    }
 
    cout << maxi << endl;
 
    return 0;
}

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