#include <bits/stdc++.h>
using namespace std;
#pragma GCC optimize("O3")
const int N=4200;
mt19937 rng(chrono::steady_clock().now().time_since_epoch().count());
bitset<N> b[N][2];
int dif[N][N];
int diff(int i, int j) {
if(dif[i][j]>=0)return dif[i][j];
return dif[i][j]=((b[i][0]^b[j][0])|(b[i][1]^b[j][1])).count();
}
int main () {
cin.tie(0)->sync_with_stdio(0);
int n, m, k;
cin >> n >> m >> k;
memset(dif, -1, sizeof dif);
string a[n];
for(int i =0 ;i<n;i++) {
cin >> a[i];
for(int j =0 ;j<m;j++) {
if(a[i][j]=='A') {
b[i][0][j]=b[i][1][j]=1;
}
else if(a[i][j]=='C') {
b[i][0][j]=1;
b[i][1][j]=0;
}
else if(a[i][j]=='G') {
b[i][0][j]=0;
b[i][1][j]=1;
}
}
}
bool check[n];
memset(check, 0, sizeof check);
queue<int> que;
for(int i = 0;i<n;i++)que.push(i);
while(que.size()>1) {
int at=que.front();
que.pop();
if(check[at])continue;
int c=rng()%n;
while(c==at) {
c=rng()%n;
}
if(diff(at, c)!=k) {
check[at]=check[c]=1;
continue;
}
else que.push(at);
}
cout << que.front()+1 << "\n";
}
