#include <iostream>
using namespace std;
#define maxn 200005

int n,k;
char a[maxn];
int sol[30];
int counter[30];

int main()
{
    int i,k,size=0,rez=0;
    cin>>n>>k;
    cin>>a;
    if(k>1)
        for(i=0;i<n-1;++i){
            if(a[i]==a[i+1]){
                counter[(a[i]%26)]++;
                if(counter[(a[i]%26)]==k-1)
                    ++sol[(a[i]%26)];
            }else
                counter[(a[i]%26)]=0;
        }
    else{
        for(i=0;i<n-1;++i)
            ++sol[(a[i]%26)];
    }
    for(i=0;i<27;++i)
        if(sol[i]>rez)
            rez=sol[i];
    cout<<rez;
}