#include <bits/stdc++.h>
using namespace std;
#define int ll
#define endl '\n' //comment for interactive
#define fast_io ios::sync_with_stdio(0); cin.tie(0); cout.tie(0)
#define pb push_back
#define re resize
#define ff first
#define ss second
#define all(x) (x).begin(), (x).end()
#define all1(x) (x).begin()+1, (x).end()
#define loop(i, n) for(int i = 0; i < n; i++)
#define loop1(i, n) for(int i = 1; i <= n; i++)
#define print(x) cout << #x << ": " << x << endl << flush
typedef long long ll;
typedef vector<int> vi;
typedef array<int, 2> ii;
typedef array<int, 3> ti;
typedef vector<ii> vii;
typedef vector<ti> vti;
typedef vector<vi> vvi;
typedef priority_queue<int> pq;
template<class T> bool ckmin(T&a, T b) { bool B = a > b; a = min(a, b); return B; }
template<class T> bool ckmax(T&a, T b) { bool B = a < b; a = max(a, b); return B; }
const int inf = 1e17;
void solve() {
int n, m, k;
cin >> n >> m >> k;
vector<string> s(n+1);
loop1(i, n) cin >> s[i];
int res = -1;
loop1(i, n) {
bool valid = true;
loop1(j, n) if(i != j) {
int cnt = 0;
loop(l, m) {
if(s[i][l] != s[j][l]) cnt++;
}
if(cnt != k) valid = false;
}
if(valid) res = i;
}
cout << res << endl;
}
signed main() {
fast_io;
int t = 1; //cin >> t;
while(t--)
solve();
return 0;
}
