#include <algorithm>
#include <bits/stdc++.h>

using namespace std;

#ifdef LOCAL
template<class... T> void dbg(T... x) { char e{}; ((cerr << e << x, e = ' '), ...); }
template<class T> void org(T l, T r) { while (l != r) cerr << ' ' << *l++; cerr << '\n'; }
#define debug(x...) dbg(#x, '=', x, '\n')
#define olist(x...) dbg(#x, '='), org(x)
#else
#define debug(...) ((void)0)
#define olist(...) ((void)0)
#endif
#define all(v) (v).begin(), (v).end()
#define rall(v) (v).rbegin(), (v).rend()
#define ff first
#define ss second

using i64 = long long;
using u64 = unsigned long long;
using i128 = __int128;
using u128 = unsigned __int128;

constexpr int inf = 1e9;
constexpr int mod = 998244353;

template<class T> bool chmin(T &a, T b) { return (b < a and (a = b, true)); }
template<class T> bool chmax(T &a, T b) { return (a < b and (a = b, true)); }
template<class... T> int add(T... x) { int t{}; return (((t += x) %= mod), ...), t; }
template<class... T> int mul(T... x) { i64 t{1}; return (((t *= x) %= mod), ...), t; }

void solve() {
    int n, m;
    cin >> n >> m;

    vector<string> S(n);
    for (auto &s : S) {
        cin >> s;
    }

    string R;
    for (int i = 0; i < m; i++) {
        array<int, 26> cnt{};
        for (int j = 0; j < n; j++) {
            cnt[S[j][i] - 'a']++;
        }
        R += max_element(all(cnt)) - cnt.begin() + 'a';
    }

    debug(R);
    int ans = 0;
    for (int i = 0; i < n; i++) {
        for (int j = 0; j < m; j++)
            ans += (R[j] != S[i][j]);
    }

    cout << ans << '\n';
        
}

signed main() {
    cin.tie(0)->sync_with_stdio(false);
    cin.exceptions(cin.failbit);
    
    int T = 1;
    // cin >> T;
    while (T--) {
        solve();
    }
    
    return 0;
}