#include<bits/stdc++.h>
using namespace std;
const long long inf = (long long) 1e18 + 10;
const int inf1 = (int) 1e9 + 10;
// #define int long long
#define dbl long double
#define endl '\n'
#define sc second
#define fr first
#define mp make_pair
#define pb push_back
#define all(x) x.begin(), x.end()
const int maxn = 4140;
mt19937 rng(143243);
int ran(int a, int b) {
return a + rng()%(b-a+1);
}
int n, m, k, a[maxn][maxn], cntcol[maxn][5], cntper[maxn][5], sumcol[maxn][5], w[maxn];
string s[maxn];
void solve() {
cin >> n >> m >> k;
for(int i = 1; i <= n; i++) {
cin >> s[i];
w[i] = ran(5,inf1);
for(int j = 0; j < m; j++) {
if(s[i][j] == 'A') a[i][j] = 0;
if(s[i][j] == 'C') a[i][j] = 1;
if(s[i][j] == 'G') a[i][j] = 2;
if(s[i][j] == 'T') a[i][j] = 3;
cntper[i][a[i][j]]++;
cntcol[j][a[i][j]]++;
sumcol[j][a[i][j]]+= w[i];
}
}
for(int i = 1; i <= n; i++) {
int sumop = 0;
for(int j = 0; j < m; j++) {
sumop+= sumcol[j][0]+sumcol[j][1]+sumcol[j][2]+sumcol[j][3]-sumcol[j][a[i][j]];
}
int sumw = 0;
for(int j = 1; j <= n; j++) {
if(i == j) continue;
sumw+= k*w[j];
}
if(sumw == sumop) {
cout << i << endl;
return;
}
}
}
int32_t main() {
ios::sync_with_stdio(false); cin.tie(0);
// freopen("in.in", "r", stdin);
// freopen("out.out", "w", stdout);
int tt = 1;
// cin >> tt;
while(tt--) {
solve();
}
}
