/// Brrrr Brrrr
#pragma GCC optimize("O3")
#pragma GCC optimize ("unroll-loops")
#pragma GCC target("avx,avx2,fma")

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

#define pb push_back
#define F first
#define S second
#define f(i, a, b)  for(int i = a; i < b; i++)
#define all(a)  a.begin(),a.end()
#define rall(a) a.rbegin(),a.rend()
#define sz(x) (int)(x).size()
#define mp(x,y) make_pair(x,y)
#define popCnt(x) (__builtin_popcountll(x))
#define int ll

using ll = long long;
using ii = pair<int, int>;
using ull = unsigned long long;

const int N = 2e5+5, LG = 18, MOD = (119 << 23) + 1;
const long double PI = acos(-1);
const long double EPS = 1e-7;

const int dx[] = {0,0,1,-1};
const int dy[] = {1,-1,0,0};

using vi = vector<int>;
using pii = pair<int, int>;

void doWork() {

    int n, m;
    cin >> n >> m;
    set<int> st;
    int ans = n*m;
    map<char,int> mp[m];
    f(i,0,n) {
        string s;
        cin >> s;
        f(j,0,m) {
            mp[j][s[j]] += 1;
        }
    }

    f(i,0,m) {
        int mx = 0;
        for(auto it : mp[i])mx = max(mx, it.S);
        ans -= mx;
    }

    cout << ans << endl;


}
int32_t main() {
#ifdef ONLINE_JUDGE
    ios_base::sync_with_stdio(0);
    cin.tie(0);
#endif // ONLINE_JUDGE


    int t = 1;
//    cin >> t;
    while (t--) {
        doWork();
    }
    return 0;
}

///Look at my code ya codeomk