#include <bits/stdc++.h>
 #define ll long long
 #define ull unsigned long long
 #define pi 3.141592654
 #define NUM 1e18
 #define Mod  1'000'000'007
 #define fixed(n) fixed<<setprecision(n)
 #define cin(v) for(auto &i:v) cin >> i ;
 #define cout(v) for(auto &i:v) cout << i  <<" ";
 #define vowel(x) (x=='e'||x=='a'||x=='i'||x=='o'||x=='u')
 #define small(x) (x>=97&&x<=122)
 #define capital(x) (x>=65&&x<=90)
 #define Tolower(s) transform(s.begin(),s.end(),s.begin(),::tolower);
 #define Toupper(s) transform(s.begin(),s.end(),s.begin(),::toupper);
 #define sz(x) (int)(x.size())
 #define all(v) ((v).begin()), ((v).end())
 #define allr(v) ((v).rbegin()), ((v).rend())
 #define updmax(a,b) a=max(a,b)
 #define updmin(a,b) a=min(a,b)
 #define ceil(a,b) ((a/b)+(a%b?1:0))
 /* asc -> 1 2 3 ,des -> 3 2 1 */

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



 void solve(){
  int n,k,maxi1=INT_MIN,counter1=0,maxi2=INT_MIN,counter2=0;
  cin>>n>>k;
  string s;
  cin>>s;
  string t=s;
  int temp1=k,temp2=k;
  char c1,c2;
  /*G*/
  for(int i=0;i<n;i++){
    temp1=k;
    if(s[i]!='G'){
      temp1--;
      counter1++;
      c1=s[i];
    }
    if(i<n-1){
      for(int j=i+1;j<n;i++){
        if(s[j]!=c1){
          counter1++;
          c1=s[j];
        }else{
          if(temp1>0){
            temp1--;
            counter1++;
            if(c1=='G'){
              s[j]=='B';
            }else{
              s[j]=='G';
            }
          }else{
            break;
          }
        }
      }
    }
    maxi1=max(maxi1,counter1);
    counter1=0;
  }
  /*B*/
  for(int i=0;i<n;i++){
    temp2=k;
    if(t[i]!='B'){
      temp2--;
      counter2++;
      c2=t[i];
    }
    if(i<n-1){
      for(int j=i+1;j<n;i++){
        if(t[j]!=c2){
          counter2++;
          c2=t[j];
        }else{
          if(temp2>0){
            temp2--;
            counter2++;
            if(c2=='B'){
              t[j]=='G';
            }else{
              t[j]=='B';
            }
          }else{
            break;
          }
        }
      }
    }
    maxi2=max(maxi2,counter2);
    counter2=0;
  }
  cout<<max(maxi1,maxi2)<<"\n";
 }

 int main(){
  Rofyda_Elghadban();
  int t=1;
  // cin>>t;
  while(t--){
    solve();
  }
  return 0;
 }