// ~ Be Name Khoda ~
// Harf ke nazanim...
// Zende bemoonim?
// Ya oonm na?
#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
#define pb push_back
#define mp make_pair
#define all(x) x.begin(), x.end()
#define fi first
#define se second
const int maxn = 1e6 + 10;
const int maxn5 = 5e5 + 10;
const int maxnt = 1.2e6 + 10;
const int maxn3 = 4102;
const int mod = 1e9 + 7;
const ll inf = 1e18;
int a[maxn3][maxn3];
ll sum[maxn3], w[maxn3];
int main()
{
ios_base::sync_with_stdio(false);cin.tie(0);cout.tie(0);
int n, m, k; cin >> n >> m >> k;
ll sumw = 0;
for(int i = 0; i < n; i++){
string s; cin >> s;
w[i] = rng() % mod + 1; sumw += w[i];
for(int j = 0; j < m; j++){
a[i][j] = (s[j] == 'A' ? 1 : -1);
sum[j] += w[i] * a[i][j];
}
}
for(int i = 0; i < n; i++){
ll ans = 0;
for(int j = 0; j < m; j++)
ans += (sum[j] - w[i] * a[i][j]) * a[i][j];
if(ans == (sumw - w[i]) * (m - 2 * k))
return cout << i + 1 << endl, 0;
}
}
