#include <bits/stdc++.h>
using namespace std;
#pragma GCC target("popcnt")
bitset<4100> b[4101]; 

void doWork(){
    int n , m , k;
    cin >> n >> m >> k;
    string s[n] = {};
    for (int i = 0 ; i < n ; i++){
        cin >> s[i]; 
        for (int j = 0 ; j < m ; j++) if (s[i][j] =='C') b[i][j] = 1; 
    } 
    for (int i = 0 ; i < n ; i++){
        bool f =1; 
        for (int j = 0 ; j < n ; j++){
            if (j == i) continue; 
            bitset<4100> c = ((b[i] ^ b[j])); 
            // cout << i << ' ' << j <<  ' ' << c.count() << '\n';
            // for (int l = 0 ; l < m ; l++) cout << b[i][l]; cout << '\n';
            // for (int l = 0 ; l < m ; l++) cout << b[j][l]; cout << '\n'; 
            // for (int l = 0 ; l < m ; l++) cout << c[l]; cout << '\n'; 
            // cout << '\n'; 
            if (c.count() != k) {f = 0;break;} 
        }
        if (f) {cout << i+1; return;}
    }
}

signed main(){
    ios::sync_with_stdio(0); cin.tie(0); cout.tie(0);
    doWork(); cout << '\n'; 
}