#include <bits/stdc++.h>
#define loop(i, a, b) for(long long i=a;i<b;i++)
#define pool(i, a, b) for(long long i=a-1;i>=b;i--)
#define fore(i, a) for(auto&& i:a)
#define fi first
#define se second
#define ps(a) push_back(a)
#define pb(a) pop_back(a)
#define sc scanf
#define vc vector
#define pa pair<ll, ll>
#define ll long long
#define lb lower_bound
#define ub upper_bound
#define all(a) a.begin(), a.end()
#define llmax LLONG_MAX/2
#define llmin -LLONG_MAX/2
using namespace std;
#define mn 510
#define pa pair<ll, ll>
#define ld long double
ll can[mn], canb[mn];
string arr[mn];
int main(){
ll n, k;cin >> n >>k;
loop(i, 1, n+1) cin >> arr[i];
loop(i, 1, n+1){
loop(j, 1, i){
ll cnt[26], cur=0;loop(z, 0, 26) cnt[z]=0;
can[0]=1, canb[n+1]=1;
loop(z, 1, n+1) can[z]=can[z-1] and (arr[i].at(z-1)==arr[j].at(z-1));
pool(z, n+1, 1) canb[z]=canb[z+1] and (arr[i].at(z-1)==arr[j].at(z-1));
loop(z, 1, n+1){
if(cnt[arr[i].at(z-1)-'a']==0) cur++;
if(cnt[arr[i].at(z-1)-'a']==-1) cur--;
cnt[arr[i].at(z-1)-'a']++;
if(cnt[arr[j].at(z-1)-'a']==0) cur++;
if(cnt[arr[j].at(z-1)-'a']==1) cur--;
cnt[arr[j].at(z-1)-'a']--;
if(z>=k and !cur and canb[z+1] and can[z-k]){
cout << "DA"<<endl;
return 0;
}
}
}
}
cout << "NE"<<endl;
return 0;
}
