#include <bits/stdc++.h>
using namespace std;
long long encode(int a, int b) {
long long sum = ((long long)a << 32) + b;
return sum;
}
int main() {
ios::sync_with_stdio(false);
cin.tie(nullptr);
int n, m, k; cin >> n >> m >> k;
vector<string> v;
unordered_map<long long,int> umap;
for (int i = 1; i <= n; i++) {
string s; cin >> s;
v.push_back(s);
for (int j = 0; j < m; j++) umap[encode(j,s[j]-'a')]++;
}
for (int i = 0; i < n; i++) {
int sum = 0;
for (int j = 0; j < m; j++) {
sum += n - (umap[encode(j,v[i][j]-'a')]);
}
if (sum == k*(n-1)) {
cout << i+1 << '\n';
return 0;
}
}
return 0;
}
