#include<cstdio>

 #include<cstring>

 #include<cmath>

 #include<string>

 #include<set>

 #include<map>

 #include<vector>

 #include<queue>

 #include<algorithm>

 #include<functional>

 #define cl(a,b) memset(a,b,sizeof(a));

 #define FFC(i,a,b) for(int i=a;i<=b;++i)

 #define pb push_back

 #define LL long long

 #define dbg puts("ok")

 #define min(a,b) ((a)>(b)?(b):(a))

 #define max(a,b) ((a)>(b)?(a):(b))

 using namespace std;

 char a[];

 int main(){

     int n,k;

     while(~scanf("%d%d",&n,&k)){

         scanf("%s",a);

         int l=,r=,ans=,ca=,cb=,tmp=;

         while(r<n){

             while(r<n&&tmp<=k){

                 if(a[r]=='a')ca++;else cb++;

                 tmp=min(ca,cb);

                 r++;

             }

             if(r==n&&tmp<=k){ans=max(r-l,ans);break;}

             r--;if(a[r]=='a')ca--;else cb--;tmp=min(ca,cb);

             ans=max(r-l,ans);

             while(a[l]==a[l+]){if(a[l]=='a')ca--;else cb--;l++,tmp=min(ca,cb);}

                 if(a[l]=='a')ca--;else cb--;l++,tmp=min(ca,cb);

         }

         printf("%d\n",ans);

     }

     return ;

 }