#include<bits/stdc++.h>
using namespace std;
#define FOR(i, a, b) for(int i = a; i < b; ++i)
#define REP(i, n) FOR(i, 0, n)
#define _ << " " <<
#define sz(x) ((int) x.size())
#define pb(x) push_back(x)
#define TRACE(x) cerr << #x << " = " << x << endl
typedef long long ll;
typedef pair<int, int> point;
const int MAXN = 505;
const int baza[8] = {1307, 991, 863, 877, 3083, 3089, 4091, 5471};
const int mod[8] = {1000000007, 1000000009, 1000000007, 1000000009, 1000000007, 1000000009, 1000000007, 1000000009};
const int brojBaza = 4;
int add(int x, int y, int id){
x += y;
if(x >= mod[id]) return x - mod[id];
if(x < 0) return x + mod[id];
return x;
}
int mul(ll x, ll y, int id){
return x * y % mod[id];
}
int n, k;
char a[MAXN][MAXN];
int hesh[MAXN][brojBaza], pot[30][brojBaza];
unordered_map<int, int> M[brojBaza];
void finish(){
cout << "DA";
exit(0);
}
void check(){
REP(i, n){
bool ok = true;
REP(j, brojBaza){
if(M[j][hesh[i][j]] <= 1){
ok = false;
break;
}
}
if(ok) finish();
}
}
int main(){
ios_base::sync_with_stdio(false); cin.tie(0);
REP(i, brojBaza)
pot[0][i] = 1;
REP(i, brojBaza)
FOR(j, 1, 30)
pot[j][i] = mul(pot[j - 1][i], baza[i], i);
cin >> n >> k;
REP(i, n) REP(j, n) cin >> a[i][j];
REP(i, n)
REP(j, brojBaza)
hesh[i][j] = a[i][0];
REP(currBase, brojBaza)
REP(i, n)
FOR(j, 1, k)
hesh[i][currBase] = add(hesh[i][currBase], pot[a[i][j] - 'a'][currBase], currBase);
REP(currBase, brojBaza)
REP(i, n)
M[currBase][hesh[i][currBase]] ++;
check();
FOR(j, k, n){
REP(currBase, brojBaza){
M[currBase].clear();
REP(i, n){
hesh[i][currBase] = add(hesh[i][currBase], pot[a[i][j] - 'a'][currBase], currBase);
hesh[i][currBase] = add( - pot[ a[i][j - k] - 'a' ][currBase] , hesh[i][currBase], currBase );
M[currBase][ hesh[i][currBase] ] ++;
}
}
check();
}
cout << "NE";
}
