//zzy2012.3.28AC#include<cstdio>#include<cstring>#include<cstdlib>#include<string>#include<cmath>#include<iostream>#include<algorithm>

using namespace std;

char chrn;#define SCRN while(scanf("%c",&chrn) && chrn!='\n');

typedef struct{int f,t,cnt;//f:最大前缀匹配的点；t：when enter the node,how many patterns are recognised；cnt 在dp时用    int e[3];}node;

typedef struct{int idx,k,n;}node2;

int N,K;int top,front,rear,queue[10000];node trie[3000];node2 Q[10000000];

void push(int i){    queue[rear++]=i;}

int pop(){    front++;return queue[front-1];}

void push2(node2 i){    Q[rear++]=i;}

node2 pop2(){    front++;return Q[front-1];}

void ini(){    top=0;    trie[0].f=-1;    trie[0].t=0;    trie[0].cnt=0;    trie[0].e[0]=-1;    trie[0].e[1]=-1;    trie[0].e[2]=-1;    top++;}

void insert(int idx,char *s,int len){if(trie[idx].e[s[0]-'A']==-1)    {        trie[idx].e[s[0]-'A']=top;        trie[top].f=0;        trie[top].cnt=-1;        trie[top].e[0]=-1;        trie[top].e[1]=-1;        trie[top].e[2]=-1;        len--;if(len==0)            trie[top++].t=1;else        {            trie[top].t=0;            top++;            insert(top-1,s+1,len);        }    }else    {        len--;if(len==0)        {            trie[trie[idx].e[s[0]-'A']].t++;return ;        }else            insert(trie[idx].e[s[0]-'A'],s+1,len);    }}

void struct_AC()//key function{int i,r,v,u;for(i=0; i<3; i++)if(trie[0].e[i]==-1)            trie[0].e[i]=0;    front=rear=0;for(i=0; i<3; i++)if(trie[0].e[i]>0)        {            trie[trie[0].e[i]].f=0;            push(trie[0].e[i]);        }while(rear>front)//struct f and t for each node    {        r=pop();for(i=0; i<3; i++)if(trie[r].e[i]>-1)            {                u=trie[r].e[i];                v=trie[r].f;while(trie[v].e[i]==-1){                    v=trie[v].f;                }                trie[u].f=trie[v].e[i];                trie[u].t+=trie[trie[v].e[i]].t;                push(u);            }    }}

int dp(){int max=0,idx,i,j,sign,t;    node2 r,u;    r.idx=0;    r.k=0;    r.n=0;    front=rear=0;    push2(r);while(rear>front)    {        r=pop2();        idx=r.idx;        t=r.n;//trie[idx].cnt;        if(t<trie[idx].cnt-1)continue;if(r.k==K-1)        {for(i=0; i<3; i++)            {if(trie[idx].e[i]>-1)                {                    j=trie[idx].e[i];if(t+trie[j].t>max)                        max=t+trie[j].t;                }else                {                    j=trie[idx].f;while(trie[j].e[i]==-1)                        j=trie[j].f;                    j=trie[j].e[i];if(t+trie[j].t>max)                        max=t+trie[j].t;                }//cout<<"__max:"<<max<<' '<<idx<<' '<<j<<' '<<r.k<<endl;            }        }else        {for(i=0; i<3; i++)if(trie[idx].e[i]>-1)                {                    j=trie[idx].e[i];if(t+trie[j].t>trie[j].cnt)                    {                        trie[j].cnt=t+trie[j].t;//cout<<"OP4---:"<<idx<<' '<<j<<' '<<r.k<<' '<<endl;                        u.idx=j;                        u.k=r.k+1;                        u.n=trie[j].cnt;//cout<<"  OP 1\n";//printf("%c\n",'A'+i);                        push2(u);                    }                }else                {                    j=trie[idx].f;while(trie[j].e[i]==-1)                        j=trie[j].f;                    j=trie[j].e[i];

if(t+trie[j].t>trie[j].cnt)                    {                        trie[j].cnt=t+trie[j].t;//cout<<"OP3: "<<idx<<" "<<j<<' '<<r.k<<' '<<endl;

                        u.idx=j;                        u.k=r.k+1;                        u.n=trie[j].cnt;//cout<<"  OP2++++++++++++++++ \n";//printf("%c\n",'A'+i);                        push2(u);                    }                }        }    }return max;}

int main(){int i,num;char s[25];//freopen("1633in.txt","r",stdin);    cin>>N>>K;    SCRN    ini();for(i=0; i<N; i++)    {        gets(s);        insert(0,s,strlen(s));    }    struct_AC();    num=dp();    cout<<num<<endl;return 0;}