//!yrt tsuj uoy srettam gnihton no emoc
#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef long double ld;
#define pb push_back
#define mp make_pair
#define pii pair <int, int>
#define fast_io ios::sync_with_stdio(false);cin.tie(0);cout.tie(0);
#define F first
#define S second
mt19937 Rnd(time(0));
const int maxn = 4100 + 5;
int n, m, k;
ll id[maxn], sm[maxn][5];
ll base = 31;
string s[maxn];
int main(){
fast_io;
cin >> n >> m >> k;
ll tot = 0;
ll x = 1;
for(int i = 0; i < n; i ++){
cin >> s[i];
id[i] = x;
x *= base;
for(int j = 0; j < m; j ++){
if(s[i][j] == 'A'){
sm[j][0] += id[i];
s[i][j] = '0';
}
else if(s[i][j] == 'C'){
sm[j][1] += id[i];
s[i][j] = '1';
}
else if(s[i][j] == 'T'){
sm[j][2] += id[i];
s[i][j] = '2';
}
else if(s[i][j] == 'G'){
sm[j][3] += id[i];
s[i][j] = '3';
}
}
tot += id[i];
}
for(int i = 0; i < n; i ++){
ll sum = 0;
for(int j = 0; j < m; j ++){
int c = s[i][j] - '0';
// cout << "c : " << c << endl;
for(int t = 0; t < 4; t ++){
if(c != t){
sum += sm[j][t];
}
}
}
// cout << i << " " << sum << " | " << (tot - id[i]) * k << endl;
if((tot - id[i]) * k == sum){
cout << i + 1;
return 0;
}
}
return 0;
}
