#include <bits/stdc++.h>
using namespace std;
struct type{
int ca,cb;
};
int main() {
int n,k;
cin>>n>>k;
string s;
cin>>s;
type aa;
aa.ca=aa.cb=0;
if(s[0]=='a')
aa.ca++;
else
aa.cb++;
vector<type>vec;
for(int i=1;i<n;i++){
if(s[i]!=s[i-1]){
vec.push_back(aa);
aa.ca=aa.cb=0;
}
if(s[i]=='a')
aa.ca++;
else
aa.cb++;
if(i==n-1){
vec.push_back(aa);
}
}
int sta=0,stb=0;
if(vec[0].ca==0){
stb=0;
for(int i=1;i<n;i++){
if(vec[i].ca>0){
sta=i;
break;
}
}
}
else if(vec[0].cb==0){
sta=0;
for(int i=1;i<n;i++){
if(vec[i].cb>0){
stb=i;
break;
}
}
}
int ans=0;
for(int i=sta;i<vec.size();i++){
if(vec[i].ca>0){
int tmp=k;
int len=vec[i].ca;
bool flag=true;
for(int j=i+1;j<n;j++){
len+=vec[j].ca;
if(vec[j].cb>0 && flag ){
if(tmp-vec[j].cb<=0 && flag){
len+=tmp;
flag=false;
}
else{
len+=vec[j].cb;
tmp-=vec[j].cb;
}
}
else if(vec[j].cb>0 && !flag){
break;
}
}
// cout<<i<<" "<<len<<endl;
ans=max(ans,len);
}
}
// cout<<endl<<endl;
for(int i=stb;i<vec.size();i++){
if(vec[i].cb>0){
int tmp=k;
int len=vec[i].cb;
bool flag=true;
for(int j=i+1;j<n;j++){
len+=vec[j].cb;
if(vec[j].ca>0 && flag ){
if(tmp-vec[j].ca<=0 && flag){
len+=tmp;
flag=false;
}
else{
len+=vec[j].ca;
tmp-=vec[j].ca;
}
}
else if(vec[j].ca>0 && !flag){
break;
}
}
//cout<<i<<" "<<len<<endl;
ans=max(ans,len);
}
}
// cout<<endl;
cout<<ans<<endl;
return 0;
}
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