#pragma GCC optimize("Ofast")
#pragma GCC optimize("unroll-loops")
#pragma GCC target("avx,avx2,fma,popcnt")
#include <bits/stdc++.h>
#define fo(i, d, c) for (int i = d; i <= c; i++)
#define fod(i, c, d) for (int i = c; i >= d; i--)
#define maxn 1000010
#define N 1010
#define fi first
#define se second
#define pb emplace_back
#define en cout << "\n";
#define bitcount(x) __builtin_popcountll(x)
#define pii pair<int, int>
#define vii vector<pii>
#define lb(x) x & -x
#define bit(i, j) ((i >> j) & 1)
#define offbit(i, j) (i ^ (1LL << j))
#define onbit(i, j) (i | (1LL << j))
#define vi vector<int>
#define all(x) x.begin(), x.end()
#define ss(x) (int)x.size()
template <typename T1, typename T2>
bool minimize(T1 &a, T2 b)
{
if (a > b)
{
a = b;
return true;
}
return false;
}
template <typename T1, typename T2>
bool maximize(T1 &a, T2 b)
{
if (a < b)
{
a = b;
return true;
}
return false;
}
using namespace std;
const int nsqrt = 450;
const int mod = 1e9 + 7;
void add(int &x, int k)
{
x += k;
x %= mod;
if(x < 0) x += mod;
}
void del(int &x, int k)
{
x -= k;
x %= mod;
if(x < 0) x += mod;
}
int n,m,k;
bitset<4100> a[16401];
short id[4111];
main()
{
#define name "TASK"
if (fopen(name ".inp", "r"))
{
freopen(name ".inp", "r", stdin);
freopen(name ".out", "w", stdout);
}
ios_base::sync_with_stdio(false);
cin.tie(NULL);
cin >> n >> m >> k;
fo(i,1,n)
{
fo(j,0,m - 1)
{
char t;
cin >> t;
if(t == 'A') a[(i - 1) * 4][j] = 1;
if(t == 'T') a[(i - 1) * 4 + 1][j] = 1;
if(t == 'G') a[(i - 1) * 4 + 2][j] = 1;
if(t == 'C') a[(i - 1) * 4 + 3][j] = 1;
}
}
fo(i,1,n) id[i] = i;
fo(i,1,n)
{
bool ok = 1;
random_shuffle(id + 1,id + n + 1);
fo(x,1,min(3 * N + 900,n))
{
int j = id[x];
if(i == j) continue;
int cnt = 0;
fo(k,0,3)
{
cnt += (a[(i - 1) * 4 + k] ^ a[(j - 1) * 4 + k]).count();
}
cnt /= 2;
if(cnt != k)
{
ok = 0;
break;
}
}
if(ok) return cout << i,0;
}
}
