#include <bits/stdc++.h>
using namespace std;
#define int long long
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
signed main(){
ios_base::sync_with_stdio(false);
cin.tie(0); cout.tie(0);
int n, m, k; cin >> n >> m >> k;
vector<int> h(n);
int allk = 0;
for(int i = 0; i < n; i++){
h[i] = uniform_int_distribution<int>(0, (1ll << 62))(rng);
allk += k * h[i];
}
vector<vector<int>> s(n, vector<int>(m));
vector<array<int, 4>> mp(m, array<int, 4>{});
for(int i = 0; i < n; i++){
for(int j = 0; j < m; j++){
char x; cin >> x;
s[i][j] = (x == 'A' ? 0 : (x == 'T' ? 1 : (x == 'G' ? 2 : 3)));
mp[j][s[i][j]] += h[i];
}
}
for(int i = 0; i < n; i++){
int sum = 0;
for(int j = 0; j < m; j++){
for(int c = 0; c < 4; c++) if(c != s[i][j]) sum += mp[j][c];
}
if(sum == allk - k * h[i]){
cout << i + 1;
return 0;
}
}
}
