/*
Editor: Abdelrahman Hossam
Nickname: Blobo2_Blobo2
IOI next year isA :)
*/
#pragma GCC optimize("Ofast,no-stack-protector,unroll-loops,fast-math,O3")
//#pragma GCC target("sse,sse2,sse3,ssse3,sse4,sse4.2,popcnt,abm,mmx,avx2,tune=native")
#pragma GCC optimize("-ffast-math")
#pragma GCC optimize("-funroll-loops")
#pragma GCC optimize("-funroll-all-loops,-fpeel-loops,-funswitch-loops")
#include<bits/stdc++.h>
using namespace std;
//#define int long long
#define endl "\n"
#define all(v) v.begin(),v.end()
#define gen(arr,n,nxt) generate(arr,arr+n,nxt)
#define Blobo2_el_7akim_elly_3ayz_yro7_IOI_w_3ayz_yakol_jilaty ios_base::sync_with_stdio(false);cin.tie(0);
#define EPS 0.00000001
const int mo=1e9+7,INF=1e18;
int nxt(){int x;cin>>x;return x;}
int rand(int l, int r){
static mt19937
rng(chrono::steady_clock::now().time_since_epoch().count());
uniform_int_distribution<int> ludo(l, r);
return ludo(rng);
}
signed main(){
Blobo2_el_7akim_elly_3ayz_yro7_IOI_w_3ayz_yakol_jilaty
freopen("in.txt","r",stdin);
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
int n=nxt(),m=nxt(),k=nxt();
string dna[n];
for(int i=0;i<n;i++)cin>>dna[i];
/*if(n<=1800){
vector<int>v;
for(int i=0;i<n;i++)
v.push_back(i);
while(v.size()>1){
int x = rand(0,v.size()-1);
for(int i=0;i<n;i++){
int ok=0;
if(i == v[x])continue;
for(int j=0;j<m;j++)
ok+= dna[v[x]][j] != dna[i][j];
if(ok != k)
goto tooooooooooooo;
}
cout<<v[x]+1;
return 0;
tooooooooooooo:;
v.erase(v.begin()+x);
}
cout<<v[0]+1;
}
else{*/
bitset<4100> a[n];
for(int i=0;i<n;i++){
for(int j=0;j<m;j++){
if(dna[i][j] == 'A')
a[i][j] =0;
else
a[i][j] =1;
}
}
vector<int>good,all;
for(int i=0;i<n;i++)
good.push_back(i),all.push_back(i);
while(good.size()>1){
shuffle(all(good),rng);
shuffle(all(all),rng);
for(int i=0;i<all.size();i++){
if(good.back() == all[i])continue;
bitset<4100>ok= (a[all[i]] ^ a[good.back()]);
if(ok.count() != k)
goto toooooooooooo;
}
cout<<good.back()+1;
return 0;
toooooooooooo:;
good.pop_back();
}
cout<<good[0]+1;
//}
return 0;
}
