E. Maximum distinct

#include <bits/stdc++.h>
#include <ext/pb_ds/tree_policy.hpp>
#include <ext/pb_ds/assoc_container.hpp>

using namespace std;
using namespace __gnu_pbds;

#define EPS 1e-9
#define PI acos(-1)
#define ll long long
#define Mod 1'000'000'007
#define INF 2'000'000'000
#define sz(x) int(x.size())
#define all(s) s.begin(), s.end()
#define rall(s) s.rbegin(), s.rend()
#define Num_of_Digits(n) ((int)log10(n)+1)
#define to_decimal(bin) stoll(bin, nullptr, 2)
#define fixed(n) cout << fixed << setprecision(n)
#define ceil(n, m) (((n) / (m)) + ((n) % (m) ? 1 : 0))
#define cout(st) for(auto& i : st) cout << i << " "; cout << "\n"
#define cout_map(mp) for(auto& [f, s] : mp) cout << f << " : " << s << "\n"
#define matrix(grid, n, m) vector < vector <int> > grid(n, vector <int> (m));
#define cout_2d(grid) for(auto& v : grid){for(auto& x : v) cout << x << " "; cout << "\n";}
#define cin_2d(grid, n, m) for(int i=0; i<n; i++) for(int j=0; j<m && cin >> grid[i][j]; j++);
#define ordered_set tree<int, null_type, less<int>, rb_tree_tag,tree_order_statistics_node_update>
#define multi_ordered_set tree<int, null_type, greater_equal<int>, rb_tree_tag,tree_order_statistics_node_update>

template < typename T = int > istream& operator >> (istream &in, vector < T > &v) {
    for (auto &x: v) in >> x;
    return in;
}

template < typename T = int > ostream& operator << (ostream &out, const vector < T > &v) {
    for (const T &x: v) out << x << ' ';
    return out;
}

void Anwar_Rizk(){
  ios_base::sync_with_stdio(false), cin.tie(nullptr), cout.tie(nullptr);
  #ifndef ONLINE_JUDGE
    freopen("input.txt", "r", stdin), freopen("output.txt", "w", stdout);
  #endif
}

void solve(){
    int n, k, ans = 0, cnt = 0;
    string s;
    cin >> n >> k >> s;
    map < char, int > occ;
    for(int i = 0; i < k; i++){
        occ[s[i]]++;
        if(occ[s[i]] == 1) cnt++;
    }
    ans = cnt;
    int l = 0, r = k;
    while(r < n){
        occ[s[r]]++;
        if(occ[s[r]] == 1) cnt++;
        occ[s[l]]--;
        if(occ[s[l]] == 0) cnt--;
        ans = max(ans, cnt);
        l++, r++;
    }
    cout << ans << "\n";
}

int main()
{   Anwar_Rizk();

    int t = 1;
    //cin >> t;
    while(t--){
      solve();
    }

  return 0;
}