#pragma GCC optimize("O3")
#pragma GCC optimize("Ofast")
#include <bits/stdc++.h>
using namespace std;
#define ssuyu                                                                  \
    ios_base::sync_with_stdio(0);                                              \
    cin.tie(0)
#define pb push_back
#define F first
#define S second
#define pii pair<int, int>
#define int long long
#define PI acos(-1)
#define all(x) (x).begin(), (x).end()
const int N = 1e6 + 5;
signed main() {
    int n, m, x, cnt = 0, cur = 2;
    char c;
    string str[105];
    int mx = -1, ans = 0;
    map<char, int> mp;
    cin >> n >> m;
    for (int i = 0; i < n; i++) {
        cin >> str[i];
    }
    for (int i = 0; i < m; i++) {
        mp.clear();
        mx = -1;
        for (int j = 0; j < n; j++) {
            mp[str[j][i]]++;
            mx = max(mx, mp[str[j][i]]);
        }
        ans += (n - mx);
    }
    cout << ans;
}