#include <cstdlib>
#include <iostream>
#include <string.h>

using namespace std;

int main(int argc, char *argv[])
{
    long int n, k, i, j, bp=1, ln, bpmaks=0;
    char r[21], kr1[21], kr2[21];
    bool is;
    scanf ("%ld %ld", &n, &k);
    scanf ("\n%s", &r);
    ln = strlen(r);
    for (i=0; i<k; i++){
        kr1[i] = r[ln-k+i];
    }
    for (i=1; i<n; i++){
        scanf ("%s", r);
        ln = strlen (r);
        is = true;
        for (j=0; j<k; j++){
            if (kr1[j] != r[j]){
               is = false;
               j = k;
            }
        }
        if (is)  bp++;
        else {
             if (bp > bpmaks) bpmaks = bp;
             bp = 1;
        }
        for (j=0; j<k; j++){
            kr1[j] = r[ln-k+j];
        }
    }
    if (bp > bpmaks) bpmaks = bp;
    printf ("%ld", bpmaks);
 //   system("PAUSE");
    return EXIT_SUCCESS;
}