#include<bits/stdc++.h>
#define endl "\n"
using namespace std;
using ll = long long;
const int maxn = 1e5 + 10;
const ll mod = 1e18 + 7;
mt19937 rnd(random_device{}());
ll seed[maxn],f[maxn][26],Hash;
string s[maxn];
void solve(void)
{
	ll n,m,k,tot=0,sum=0;
	cin>>n>>m>>k;
	for(int i=1;i<=n;i++)
	{
		cin>>s[i];
		seed[i]=rnd()%mod;
		s[i]=" "+s[i];
		for(int j=1;j<=m;j++)
		{
			(f[j][s[i][j]-'A']+=seed[i])%=mod;
			(tot+=seed[i])%=mod;
		}
		(Hash+=k*seed[i])%=mod;
	}
	for(int i=1;i<=n;i++)
	{
		sum=0;
		for(int j=1;j<=m;j++)
		{
			(sum+=f[j][s[i][j]-'A'])%=mod;
		}
		if(((tot-sum)%mod+mod)%mod==((Hash-k*seed[i]%mod)%mod+mod)%mod)
		{
			cout<<i<<endl;
			break;
		}
	}
}
int main(void)
{
	ios::sync_with_stdio(false);
	cin.tie(0);
	cout.tie(0);
	int t=1;
	while(t--)
	{
		solve();
	}
	return 0;
}