#include <iostream>
#include <fstream>
#include <string>
#include <vector>
#include <cstring>

using namespace std;

ifstream f("paznici.in");
ofstream g("paznici.out");

const int maxn = 30;

vector <int> nod[maxn];
string s;
int n, m, i, j, cup;
int viz[maxn], ok;
int r[maxn], l[maxn];
int a1[maxn], a2[maxn];

bool match(int x) {
    if(viz[x] != 0) { return false; }
    viz[x] = 1;
    for(auto u : nod[x]) {
        if(l[u] == false) {
            l[u] = x;
            r[x] = u;
            return true;
        }
    }
    for(auto u : nod[x]) {
        if(match(l[u]) == true) {
            l[u] = x;
            r[x] = u;
            return true;
        }
    }
    return false;
}

void dfs(int x) {
    viz[x] = 1;
    a1[x] = 0;
    for(auto u : nod[x]) {
        if(viz[r[u]] == 0) {
            a2[u] = true;
            dfs(u);
        }
    }
}

int main()
{
    f >> n >> m;
    for(i = 1; i <= n; i ++) {
        f >> s;
        for(j = 0; j < m; j ++) {
            if(s[j] == '1') {
                nod[i].push_back(j + 1);
            }
        }
    }

    do {
        ok = false;
        memset(viz, 0, sizeof(viz));
        for(i = 1; i <= n; i ++) {
            if(l[i] == 0 && match(i) == true) {
                ++cup;
                ok = true;
            }
        }
    } while(ok == true);

    for(i = 1; i <= n; i ++) {
        if(l[i] != 0) {
            a1[i] = true;
            viz[i] = true;
        }
    }

    for(i = 1; i <= n; i ++) {
        if(l[i] == 0) {
            dfs(i);
        }
    }

    for(i = 1; i <= n; i ++) {
        if(a1[i] == true) {
            g << (char)(i + 'A' + 1);
        }
    }
    for(i = 1; i <= n; i ++) {
        if(a2[i] == true) {
            g << (char)(i + 'a' + 1);
        }
    }

    f.close(); g.close();
    return 0;
}