#include <bits/stdc++.h>

using namespace std;
using ll = long long;
// #define int ll
using PII = pair<ll, ll>;

#define FOR(i, a, n) for (ll i = (ll)a; i < (ll)n; ++i)
#define REP(i, n) FOR(i, 0, n)
#define ALL(x) x.begin(), x.end()

template<typename T> T &chmin(T &a, const T &b) { return a = min(a, b); }
template<typename T> T &chmax(T &a, const T &b) { return a = max(a, b); }
template<typename T> bool IN(T a, T b, T x) { return a<=x&&x<b; }
template<typename T> T ceil(T a, T b) { return a/b + !!(a%b); }

template<typename T> vector<T> make_v(size_t a) { return vector<T>(a); }
template<typename T,typename... Ts>
auto make_v(size_t a,Ts... ts) {
    return vector<decltype(make_v<T>(ts...))>(a,make_v<T>(ts...));
}
template<typename T,typename V> typename enable_if<is_class<T>::value==0>::type
fill_v(T &t, const V &v) { t=v; }
template<typename T,typename V> typename enable_if<is_class<T>::value!=0>::type
fill_v(T &t, const V &v ) { for(auto &e:t) fill_v(e,v); }

template<class S,class T>
ostream &operator <<(ostream& out,const pair<S,T>& a) {
    out<<'('<<a.first<<','<<a.second<<')'; return out;
}
template<class T>
ostream &operator <<(ostream& out,const vector<T>& a){
    out<<'[';
    for(const T &i: a) out<<i<<',';
    out<<']';
    return out;
}
template<class T>
ostream &operator <<(ostream& out, const set<T>& a) {
    out<<'{';
    for(const T &i: a) out<<i<<',';
    out<<'}';
    return out;
}
template<class T, class S>
ostream &operator <<(ostream& out, const map<T,S>& a) {
    out<<'{';
    for(auto &i: a) out<<i<<',';
    out<<'}';
    return out;
}

int dx[] = {0, 1, 0, -1}, dy[] = {1, 0, -1, 0}; // DRUL
const int INF = 1<<30;
const ll LLINF = 1LL<<60;
const ll MOD = 1000000007;

signed main(void)
{
    cin.tie(0);
    ios::sync_with_stdio(false);

    while(1) {
        ll n, m;
        cin >> n >> m;
        if(!n) break;
        vector<string> a(n);
        REP(i, n) cin >> a[i];

        if(n <= 21) {
            int ans = 0;
            REP(i, 1LL<<n) {
                int sz = __builtin_popcount(i);
                if(ans >= sz) continue;
                vector<int> cnt(m);
                REP(j, n) {
                    if(i&1LL<<j) {
                        REP(k, m) if(a[j][k]=='1') cnt[k] ^= 1;
                    }
                }
                bool flag = true;
                REP(k, m) if(cnt[k] == 1) flag = false;
                if(flag) chmax(ans, sz);
            }
            cout << ans << endl;
        } else {
            vector<int> b(n);
            REP(i, n) {
                REP(j, m) {
                    b[i] *= 2;
                    b[i] += a[i][j]-'0';
                }
            }

            ll cur = 0, nxt = 1;
            vector<vector<int>> dp(2, vector<int>(1LL<<m, -INF));
            dp[0][0] = 0;
            REP(i, n) {
                dp[nxt].assign(1LL<<m, -INF);
                REP(j, 1LL<<m) {
                    if(dp[cur][j] == -LLINF) continue;
                    chmax(dp[nxt][j^b[i]], dp[cur][j] + 1);
                    chmax(dp[nxt][j], dp[cur][j]);
                }
                swap(cur, nxt);
            }
            cout << dp[cur][0] << endl;
        }
    }

    return 0;
}



Measured memory_bytes: 52224