#include <bits/stdc++.h>
using namespace std;

int main() {
    ios::sync_with_stdio(false);
    cin.tie(0);

    int n, m, k;
    cin >> n >> m >> k;

    char students[701][701];

    for(int i = 0; i < n; i++) {
        cin >> students[i];
    }

    bool closed[26] = { false };
    
    int res = 0;

    for(int i = 0; i < m; i++) {
        bool tempClosed[26] = { false };
        bool successful = true;

        for(int j = 0; j < n; j++) {
            int classIndex = students[j][i] - 'A';
            tempClosed[classIndex] = true;
            if (closed[classIndex]) {
                successful = false;
            }
        }

        res += successful;

        for(int j = 0; j < 26; j++) {
            closed[j] = closed[j] || tempClosed[j];
        }
    }

    cout << res << endl;
}