#include<bits/stdc++.h>
#define fi first
#define se second
#define int long long
using namespace std;
using db=double;
using sll=__int128;
using lb=long double;
int32_t main(){
ios::sync_with_stdio(0); cin.tie(0); cout.tie(0); srand(time(0));
int n,m,k; cin>>n>>m>>k; vector<string>a(n+1);
for(int i=1; i<=n; i++){ cin>>a[i]; }
const int MAXN=1805; vector<bitset<MAXN>>A(n+1);
for(int i=1; i<=n; i++){
for(int j=0; j<m; j++){
if(a[i][j]=='A')A[i][j]=1;
}
}
int ans=-1;
for(int i=1; i<=n; i++){
bool ok=true;
for(int j=1; j<=n; j++){
if(i==j)continue;
if((A[i]^A[j]).count()!=k)ok=false;
}
if(ok)ans=i;
}
cout<<ans<<'\n';
}
/*
O what can ail thee, knight-at-arms,
Alone and palely loitering?
The sedge has withered from the lake,
And no birds sing.
O what can ail thee, knight-at-arms,
So haggard and so woe-begone?
The squirrel’s granary is full,
And the harvest’s done.
I see a lily on thy brow,
With anguish moist and fever-dew,
And on thy cheeks a fading rose
Fast withereth too.
*/
