#include <vector>

#include <cstdio>
#include <cstring>
using namespace std;

const int MAX_N = 30;

int N1, N2;
int L[MAX_N], R[MAX_N];
vector < int > v[MAX_N];
char S[100];
bool used[MAX_N], SL[MAX_N], SR[MAX_N];

inline void support(int x) {
    for(size_t i = 0; i < v[x].size(); ++i) {
        int y = v[x][i];
        if(SR[y])
            continue;
        SR[y] = 1;
        SL[R[y]] = 0;
        support(R[y]);
    }
}

inline bool pair_up(int x) {
    if(used[x])
        return 0;
    used[x] = 1;
    for(size_t i = 0; i < v[x].size(); ++i) {
        int y = v[x][i];
        if(!R[y] || pair_up(R[y])) {
            L[x] = y;
            R[y] = x;
            return 1;
        }
    }
    return 0;
}

int main() {
    FILE *f, *g;
    f = fopen("paznici.in", "r");
    g = fopen("paznici.out", "w");

    fscanf(f, "%d %d", &N1, &N2);
    fgets(S, 3, f);
    for(int i = 1; i <= N1; ++i) {
        fgets(S, 95, f);
        for(int j = 0; j < N2; ++j)
            if(S[j] == '1')
                v[i].push_back(j+1);
    }

    int ok = 1;
    while(ok) {
        memset(used, 0, sizeof(used));
        ok = 0;
        for(int i = 1; i <= N1; ++i)
            if(!L[i] && pair_up(i))
                ok = 1;
    }

    for(int i = 1; i <= N1; ++i)
        if(L[i])
            SL[i] = 1;
    for(int i = 1; i <= N1; ++i)
        if(!L[i])
            support(i);

    for(int i = 1; i <= N1; ++i)
        if(SL[i])
            fprintf(g, "%c", i+'A'-1);
    for(int i = 1; i <= N2; ++i)
        if(SR[i])
            fprintf(g, "%c", i+'a'-1);
    fprintf(g, "\n");

    fclose(f);
    fclose(g);

    return 0;
}