#include<bits/stdc++.h>
using namespace std;
using ll=long long;
ll n,m,k;
string s[5005];
ll cnt[5005][4];
int cv(char c){
if(c=='A')return 0;
else if(c=='C')return 1;
else if(c=='G')return 2;
return 3;
}
int main(){
ios::sync_with_stdio(false);
cin.tie(nullptr);
cout.tie(nullptr);
cin>>n>>m>>k;
srand(time(nullptr));
vector<int>v(n+1,0);
ll sv=0;
for(int i=1;i<=n;++i){
cin>>s[i];
v[i]=rand()%((int)1e9);
for(int j=0;j<m;++j){
int c=cv(s[i][j]);
cnt[j][c]+=v[i];
}
sv+=v[i];
}
vector<int>ch;
for(int i=1;i<=n;++i){
ll ss=0;
for(int j=0;j<m;++j){
int c=cv(s[i][j]);
for(int k=0;k<=3;++k)
if(k!=c)
ss+=cnt[j][k];
}
if(ss==k*(sv-v[i]))ch.push_back(i);
}
cout<<ch[0]<<'\n';
}
