#include <bits/stdc++.h>
#define ZAZO ios::sync_with_stdio(0);cin.tie(0);cout.tie(0);
using namespace std;
// i have maximum 65 chuncks , each chuck will have 64 bits (elements)
unsigned long long bits[4100][65],bits2[4100][65];
int n , m , k ;
bool check(int x , int y)
{
int cnt=0;
for(int i = 0 ; i < 65 ; i++)
cnt += __builtin_popcountll((bits[x][i]^bits[y][i])|(bits2[x][i]^bits2[y][i]));
if(cnt == k) return true;
return false;
}
int32_t main() {
ZAZO
cin >> n >> m >> k;
for(int i = 0 ; i < n ; i++)
{
for(int j = 0 ; j < m ; j ++)
{
char s; cin >> s;
// get the bit you want by checking mod
unsigned long long pos = ((unsigned long long) 1<<j%64);
// set the bit to one in the specific place in the specific chunk;
if(s == 'C') bits[i][j/64] |= pos;
else if(s == 'T') bits[i][j/64] |= pos , bits2[i][j/64] |= pos;
else if(s == 'G') bits2[i][j/64] |= pos;
}
}
int ans[n]={0};
for(int i = 0 ; i < n ; i ++)
{
/// if(ans[i]==-1) continue;
for(int j = i+1 ; j < n ; j ++)
{
bool ok = check(i , j);
if(ok)
{
ans[i]++; ans[j]++;
if(ans[i] == n-1) {
cout<<i+1;
return 0;
}
if(ans[j] == n-1){
cout<<j+1;
return 0;
}
}
else{
ans[i]=-1;
ans[j]=-1;
// break;
}
}
}
}
