#include <stdio.h>
#include <bits/stdc++.h>
#include <atcoder/all>
using namespace atcoder;
using mint = modint998244353;
using namespace std;
#define rep(i,n) for (int i = 0; i < (n); ++i)
#define Inf32 1000000000
#define Inf64 1000000000000000001LL

template <class S>
struct potentialized_dsu {
  public:
    potentialized_dsu() : _n(0) {}
    potentialized_dsu(int n) : _n(n), parent_or_size(n, -1), d(n) {}

    int merge(int a, int b, S v) {
        assert(0 <= a && a < _n);
        assert(0 <= b && b < _n);
        int x = leader(a), y = leader(b);
        if (x == y) return x;
		
		if (-parent_or_size[x] < -parent_or_size[y]){
			std::swap(x, y);
			std::swap(a, b);
			S t;
			v = t - v;
		}
		
		v += diff(x,a);
		v -= diff(y,b);
		
		d[y] += d[x] + v;
		
        parent_or_size[x] += parent_or_size[y];
        parent_or_size[y] = x;
		
        return x;
    }

    bool same(int a, int b) {
        assert(0 <= a && a < _n);
        assert(0 <= b && b < _n);
        return leader(a) == leader(b);
    }

    int leader(int a) {
        assert(0 <= a && a < _n);
        if (parent_or_size[a] < 0) return a;
		int l = leader(parent_or_size[a]);
		if(parent_or_size[a] != l){
			d[a] += d[parent_or_size[a]];
			parent_or_size[a] = l;
		}
        return parent_or_size[a];
    }

    int size(int a) {
        assert(0 <= a && a < _n);
        return -parent_or_size[leader(a)];
    }
	
	S diff(int a,int b){
		assert(0 <= a && a < _n);
		assert(0 <= b && b < _n);
		leader(a);
		leader(b);
		return d[b] - d[a];
	}

    std::vector<std::vector<int>> groups() {
        std::vector<int> leader_buf(_n), group_size(_n);
        for (int i = 0; i < _n; i++) {
            leader_buf[i] = leader(i);
            group_size[leader_buf[i]]++;
        }
        std::vector<std::vector<int>> result(_n);
        for (int i = 0; i < _n; i++) {
            result[i].reserve(group_size[i]);
        }
        for (int i = 0; i < _n; i++) {
            result[leader_buf[i]].push_back(i);
        }
        result.erase(
            std::remove_if(result.begin(), result.end(),
                           [&](const std::vector<int>& v) { return v.empty(); }),
            result.end());
        return result;
    }

  private:
    int _n;
    // root node: -1 * component size
    // otherwise: parent
    std::vector<int> parent_or_size;
	std::vector<S> d;
};

struct xorint{
	using mytype = xorint;
	int v = 0;
	mytype operator+(mytype another)const{
		return (mytype(*this)+=another);
	}
	
	mytype &operator+=(const mytype &another){
		(*this).v ^= another.v;
		return (*this);
	}
	
	mytype operator-(mytype another)const{
		return (mytype(*this)-=another);
	}
	
	mytype &operator-=(const mytype &another){
		(*this).v ^= another.v;
		return (*this);
	}
};
int main(){
	
	int h,w;
	cin>>h>>w;
	vector<string> s(h);
	rep(i,h)cin>>s[i];
	
	sort(s.begin(),s.end(),[&](string a,string b){
		int x = 0,y = 0;
		rep(i,w){
			if(a[i]=='1')x++;
			if(b[i]=='1')y++;
		}
		if(x!=y)return x<y;
		return a<b;
	});
	scc_graph S(h);
	vector<int> u,v;
	rep(i,h){
		for(int j=i+1;j<h;j++){
			if(s[i]==s[j]){
				S.add_edge(i,j);
				S.add_edge(j,i);
			}
			else{
				bool f = true;
				rep(k,w){
					if(s[i][k]=='1' && s[j][k]=='0')f = false;
				}
				if(f){
					S.add_edge(i,j);
					u.push_back(i);
					v.push_back(j);
				}
			}
		}
	}
	auto ss = S.scc();
	vector<int> pos(h);
	rep(i,ss.size()){
		for(auto j:ss[i]){
			pos[j] = i;
		}
	}
	vector<vector<int>> E(ss.size());
	rep(i,u.size()){
		E[pos[u[i]]].push_back(pos[v[i]]);
	}
	vector<int> dp(ss.size(),0);
	rep(i,ss.size()){
		dp[i] += ss[i].size();
		rep(j,E[i].size()){
			dp[E[i][j]] = max(dp[E[i][j]],dp[i]);
		}
	}
	int ans = 0;
	rep(i,ss.size()){
		ans = max(ans,dp[i]);
	}
	cout<<h-ans<<endl;
	return 0;
}