#include<bits/stdc++.h>
using namespace std;
#define pb push_back
#define st first
#define nd second
#define pii pair<int, int>
#define all(x) (x).begin(), (x).end()
#define sz(x) (int)(x).size()
vector<int> tab[4109];
bool vis[4109];
queue<int> Q;
int dp[4109][4109];
int ile[4109][4];
int sum[4109];
int32_t main() {
ios_base::sync_with_stdio(false);
cin.tie(NULL);
memset(dp, -1, sizeof(dp));
int n, m, K;
cin >> n >> m >> K;
for(int i=1;i<=n;i++) {
tab[i].resize(m);
string s;
cin >> s;
for(int j=0;j<m;j++) {
if(s[j]=='A') {
tab[i][j] = 0;
} else if(s[j] == 'C') {
tab[i][j] = 1;
} else if(s[j] == 'G') {
tab[i][j] = 2;
} else {
tab[i][j] = 3;
}
}
}
for(int i=1;i<=n;i++) {
for(int j=0;j<m;j++) {
ile[j][tab[i][j]]++;
}
}
for(int i=1;i<=n;i++) {
for(int j=0;j<m;j++) {
for(int k=0;k<4;k++) {
if(tab[i][j]!=k) {
sum[i]+=ile[j][k];
}
}
}
}
for(int i=1;i<=n;i++) {
if(sum[i]!=K*(n-1)) vis[i] = true;
}
vector<int> v;
for(int i=1;i<=n;i++) v.pb(i);
for(int i=1;i<=n;i++) {
if(!vis[i]) {
Q.push(i);
vis[i] = true;
break;
}
}
random_shuffle(all(v));
while(true) {
int x = Q.front();
Q.pop();
bool ans = true;
for(int i=0;i<n;i++) {
if(v[i]==x) continue;
int cnt = dp[v[i]][x];
if(cnt==-1) {
cnt = 0;
for(int j=0;j<m;j++) {
if(tab[x][j]!=tab[v[i]][j]) cnt++;
}
}
dp[v[i]][x] = dp[x][v[i]] = cnt;
if(cnt==K) {
if(!vis[v[i]]) {
vis[v[i]] = true;
Q.push(v[i]);
}
} else {
vis[v[i]] = true;
ans = false;
}
}
if(ans) {
cout << x << "\n";
return 0;
}
}
}
