#include<iostream>

#include<cstdio>

#include<cstring>

#define re register

using namespace std;

int max(int &a,int &b){return a>b?a:b;}

int n,k,ans,f[][][];

char a[];

int main(){

    scanf("%d%d",&n,&k);

    scanf("%s",a+);

    memset(f,,sizeof(f));//初始化极小值

    f[][][]=f[][][]=f[][a[]=='j'][a[]=='z']=;

    for(re int i=;i<=n;++i)

        for(re int j=;j<=k;++j)

            for(re int u=;u<=k;++u){

                f[i][j][u]=f[i-][j][u];

                if(a[i-]=='j'&&a[i]=='z') f[i][j][u]=max(f[i][j][u],f[i-][j][u]+);

                if(j&&a[i-]=='j'&&a[i]=='j') f[i][j][u]=max(f[i][j][u],f[i-][j-][u]+);

                if(u&&a[i-]=='z'&&a[i]=='z') f[i][j][u]=max(f[i][j][u],f[i-][j][u-]+);

                if(j&&u&&a[i-]=='z'&&a[i]=='j') f[i][j][u]=max(f[i][j][u],f[i-][j-][u-]+);

            }

    for(re int i=;i<=k;++i) ans=max(ans,f[n][i][i]);//交换就是'j','z'修改的个数相同

    printf("%d",ans);

    return ;

}