#include <bits/stdc++.h>
#pragma GCC optimize("O3")
using namespace std;
typedef long long ll;
typedef string str;
typedef vector<int> vi;
typedef vector<bool> vb;
typedef set<int> si;
typedef vector<vi> vvi;
typedef vector<str> vs;
int operator*(vi &a, vi &b){
int ans = 0;
for(int i = 0;i < a.size();i++) ans += a[i]*b[i];
return ans;
}
vi operator+(vi &a, vi &b){
vi v(a.size());
for(int i = 0;i < a.size();i++) v[i] = a[i] + b[i];
return v;
}
vi operator-(vi &a, vi &b){
vi v(a.size());
for(int i = 0;i < a.size();i++) v[i] = a[i] - b[i];
return v;
}
int prob(int N, int M, int K, vs &D){
vvi V(N,vi(3*M));
for(int i = 0;i < N;i++){
for(int j = 0;j < M;j++){
V[i][3*j] = (D[i][j] == 'A' ? 1 : -1);
V[i][3*j+1] = (D[i][j] == 'T' ? 1 : -1);
V[i][3*j+2] = (D[i][j] == 'C' ? 1 : -1);
if(D[i][j] == 'G') V[i][3*j] = V[i][3*j+1] = V[i][3*j+2] = 1;
}
}
int num_left = N, num_curr = 0, num_curr2;
vi sum, sum2;
vb left(N,1), curr=left;
int K2 = 3*M - 4*K;
for(;num_left > 1;num_curr = 0){
sum.assign(3*M,0);
for(int i = 0;i < N;i++){
curr[i] = rand()%2;
if(!curr[i]) continue;
sum = sum + V[i];
num_curr++;
}
for(int i = 0;i < N;i++){
if(!left[i]) continue;
num_curr2 = num_curr - curr[i];
sum2 = curr[i] ? sum - V[i] : sum;
if(V[i] * sum2 == K2 * num_curr2) continue;
left[i] = 0;
num_left--;
}
}
return find(left.begin(),left.end(),true) - left.begin();
}
int main(){
int N,M,K;
cin >> N >> M >> K;
vs D(N);
for(int i = 0;i < N;i++) cin >> D[i];
cout << (prob(N,M,K,D) + 1);
return 0;
}
