#include <bits/stdc++.h>
using namespace std;
 
int main() {
	// your code goes here
	int n;
	cin>>n;
	int k;
	cin>>k;
	string s;
	cin>>s;
	int maxi=0;
	multiset<int>arr;     //keep the character in sorted way
	int i=0;
	for(int j=0;j<n;j++){
		arr.insert(s[j]);
		int diff=*arr.rbegin()-*arr.end();
		while(diff>k){
			arr.erase(s[i]);
		    diff=*arr.rbegin()-*arr.end();
		    i++;
		}
		int len=j-i+1;
		maxi=max(maxi,len);
 
	}
	cout<<"The largest valid substring is:"<<maxi;
 
	return 0;
}

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

NwphYmFjYWJhCjI=

7
abacaba
2