#include <bits/stdc++.h>
using namespace std;
const int BUFFER_SIZE = 1 << 20;
char input_buffer[BUFFER_SIZE];
int input_pos = 0, input_len = 0;
inline char nextChar() {
if (input_pos == input_len) {
input_pos = 0;
input_len = fread(input_buffer, 1, BUFFER_SIZE, stdin);
if (input_len == 0) return EOF;
}
return input_buffer[input_pos++];
}
inline void fast_read(int &x) {
x = 0;
char c;
bool neg = false;
do {
c = nextChar();
} while (c != '-' && (c < '0' || c > '9'));
if (c == '-') {
neg = true;
c = nextChar();
}
while (c >= '0' && c <= '9') {
x = x * 10 + (c - '0');
c = nextChar();
}
if (neg) x = -x;
}
inline void fast_read(string &s) {
s.clear();
char c;
do {
c = nextChar();
if (c == EOF) return;
} while (c == ' ' || c == '\n' || c == '\r' || c == '\t');
for (; c != EOF && c != ' ' && c != '\n' && c != '\r' && c != '\t'; c = nextChar()) {
s.push_back(c);
}
}
bitset<4101> t[4101];
bitset<4101> t1[4101];
bitset<4101> t2[4101];
bitset<4101> t3[4101];
int res[4101];
signed main()
{
ios_base::sync_with_stdio(false);
cin.tie(nullptr);
int a, b, c;
fast_read(a);
fast_read(b);
fast_read(c);
for (int i = 1; i <= a; i++) {
string s;
fast_read(s);
for (int j = 0; j < b; j++) {
if (s[j]=='A'){
t[i][j]=1;
}else if (s[j]=='T'){
t1[i][j]=1;
}else if (s[j]=='G'){
t2[i][j]=1;
}else{
t3[i][j]=1;
}
}
}
for (int i = 1; i <= a; i++) {
bool check=true;
for (int j = i + 1; j <= a; j++) {
if ((t[i] ^ t[j]).count()+(t1[i] ^ t1[j]).count()+(t2[i] ^ t2[j]).count()+(t3[i] ^ t3[j]).count() == 2*c) {
}else{
check=false;
break;
}
}
if (check){
cout << i << "\n";
return 0;
}
}
return 0;
}
