#include <bits/stdc++.h>
using namespace std;
using ll=long long;
const ll ILL=2167167167167167167;
const int INF=2100000000;
#define rep(i,a,b) for (int i=(int)(a);i<(int)(b);i++)
#define all(p) p.begin(),p.end()
template<class T> using _pq = priority_queue<T, vector<T>, greater<T>>;
template<class T> int LB(vector<T> &v,T a){return lower_bound(v.begin(),v.end(),a)-v.begin();}
template<class T> int UB(vector<T> &v,T a){return upper_bound(v.begin(),v.end(),a)-v.begin();}
template<class T> bool chmin(T &a,T b){if(b<a){a=b;return 1;}else return 0;}
template<class T> bool chmax(T &a,T b){if(a<b){a=b;return 1;}else return 0;}
template<class T> void So(vector<T> &v) {sort(v.begin(),v.end());}
template<class T> void Sore(vector<T> &v) {sort(v.begin(),v.end(),[](T x,T y){return x>y;});}
bool yneos(bool a,bool upp=false){if(a){cout<<(upp?"YES\n":"Yes\n");}else{cout<<(upp?"NO\n":"No\n");}return a;}
template<class T> void vec_out(vector<T> &p,int ty=0){
    if(ty==2){cout<<'{';for(int i=0;i<(int)p.size();i++){if(i){cout<<",";}cout<<'"'<<p[i]<<'"';}cout<<"}\n";}
    else{if(ty==1){cout<<p.size()<<"\n";}for(int i=0;i<(int)(p.size());i++){if(i) cout<<" ";cout<<p[i];}cout<<"\n";}}
template<class T> T vec_min(vector<T> &a){assert(!a.empty());T ans=a[0];for(auto &x:a) chmin(ans,x);return ans;}
template<class T> T vec_max(vector<T> &a){assert(!a.empty());T ans=a[0];for(auto &x:a) chmax(ans,x);return ans;}
template<class T> T vec_sum(vector<T> &a){T ans=T(0);for(auto &x:a) ans+=x;return ans;}
int pop_count(long long a){int res=0;while(a){res+=(a&1),a>>=1;}return res;}
template<class T> T square(T a){return a * a;}

vector< int > maximum_independent_set(const vector<vector<int>> &g, int trial = 1000000) {

    int N = (int) g.size();
    vector< uint64_t > bit(N);

    assert(N <= 64);
    for(int i = 0; i < N; i++) {
        for(int j = 0; j < N; j++) {
            if(i != j) {
                assert(g[i][j] == g[j][i]);
                if(g[i][j]) bit[i] |= uint64_t(1) << j;
            }
        }
    }

    vector< int > ord(N);
    iota(begin(ord), end(ord), 0);
    mt19937 mt(chrono::steady_clock::now().time_since_epoch().count());
    int ret = 0;
    uint64_t ver;
    for(int i = 0; i < trial; i++) {
        shuffle(begin(ord), end(ord), mt);
        uint64_t used = 0;
        int add = 0;
        for(int j : ord) {
            if(used & bit[j]) continue;
            used |= uint64_t(1) << j;
            ++add;
        }
        if(ret < add) {
            ret = add;
            ver = used;
        }
    }
    vector< int > ans;
    for(int i = 0; i < N; i++) {
        if((ver >> i) & 1) ans.emplace_back(i);
    }
    return ans;
}

void solve();
// CITRUS CURIO CITY / FREDERIC
int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);

    int t = 1;
    // cin >> t;
    rep(i, 0, t) solve();
}

void solve(){
    int N, M;
    cin >> N >> M;
    vector G(N, vector<int>(N));
    vector<string> S(N);
    rep(i, 0, N) cin >> S[i];
    rep(i, 0, N) rep(j, i + 1, N){
        int A = 0, B = 0;
        rep(k, 0, M){
            if (S[i][k] == '1' && S[j][k] == '0') A = 1;
            if (S[i][k] == '0' && S[j][k] == '1') B = 1;
        }
        if (min(A, B)){
            G[i][j] = 1;
            G[j][i] = 1;
        }
    }
    auto tmp = maximum_independent_set(G);
    cout << N - (int)tmp.size() << "\n";
}