using System;
using System.Linq;
using System.Collections.Generic;
using Debug = System.Diagnostics.Debug;
using SB = System.Text.StringBuilder;
using System.IO;
using Number = System.Int64;
namespace Program {
    public class Solver {


        public void Solve() {
            var ord = new char[52];
            for (int i = 0; i < 26; i++) {
                ord[i] = (char)(i + 'a');
                ord[i + 26] = (char)(i + 'A');
            }
            ord = ord.OrderBy(x => x.ToString(), StringComparer.Ordinal).ToArray();

            for (; ; ) {
                var n = ri;
                var d = ri;
                if (n == 0) return;
                var s = Enumerate(3, x => rs);
                var a = 0; var b = 0; var c = 0; var v = 0;

                for (int i = 0; i < n; i++) {
                    var ch = Enumerate(3, x => s[x][i]);
                    if (ch.Distinct().Count() == 2) {
                        if (ch[0] == ch[1]) c++;
                        else if (ch[0] == ch[2]) b++;
                        else a++;
                    }
                    else if (ch.Distinct().Count() == 3) v++;
                }
                var D = Enumerate(3, x => d);
                Func<int[], bool> check = (X) => {
                    if (X.Min() < 0) return false;
                    var u = new int[3];
                    u[0] = v + a - X[0];
                    u[1] = v + b - X[1];
                    u[2] = v + c - X[2];
                    if (u.Sum(x => Math.Max(0, x)) <= v) return true;
                    if (u.Count(x => x > 0) >= 2) return false;
                    var mi = -u.Where(x => x <= 0).Max();
                    return u.Select(x => x <= 0 ? x + mi : x - mi).Sum(x => Math.Max(0, x)) <= v;
                };
                var ans = Enumerate(n, x => '#');
                for (int i = 0; i < n; i++) {
                    var ch = Enumerate(3, x => s[x][i]);
                    if (ch.Distinct().Count() == 2) {
                        if (ch[0] == ch[1]) c--;
                        else if (ch[0] == ch[2]) b--;
                        else a--;
                    }
                    else if (ch.Distinct().Count() == 3) v--;
                    for (int j = 0; j < 52; j++) {
                        if (j != 0 && ch.All(x => x != ord[j])) continue;
                        var E = D.ToArray();
                        for (int k = 0; k < 3; k++)
                            if (s[k][i] != ord[j]) E[k]--;
                        if (!check(E)) continue;
                        D = E;
                        ans[i] = ord[j];
                        break;
                    }
                    if (ans[i] == '#') { Console.WriteLine(-1); break; }
                }
                if (ans[n - 1] != '#') Console.WriteLine(ans);
            }
        }


        const long INF = 1L << 60;
        //int[] dx = { -1, 0, 1, 0 };
        //int[] dy = { 0, 1, 0, -1 };
        //*
        int ri { get { return sc.Integer(); } }
        long rl { get { return sc.Long(); } }
        double rd { get { return sc.Double(); } }
        string rs { get { return sc.Scan(); } }
        //*/

        public IO.StreamScanner sc = new IO.StreamScanner(Console.OpenStandardInput());
        static T[] Enumerate<T>(int n, Func<int, T> f) { var a = new T[n]; for (int i = 0; i < n; ++i) a[i] = f(i); return a; }
        static public void Swap<T>(ref T a, ref T b) { var tmp = a; a = b; b = tmp; }
    }
}

#region main
static class Ex {
    static public string AsString(this IEnumerable<char> ie) { return new string(ie.ToArray()); }
    static public string AsJoinedString<T>(this IEnumerable<T> ie, string st = " ") {
        return string.Join(st, ie.Select(x => x.ToString()).ToArray());
        //return string.Join(st, ie);
    }
    static public void Main() {
        Console.SetOut(new System.IO.StreamWriter(Console.OpenStandardOutput()) { AutoFlush = false });
        var solver = new Program.Solver();
        solver.Solve();
        Console.Out.Flush();
    }
}
#endregion
#region Ex
namespace Program.IO {
    using System.IO;
    using System.Text;
    using System.Globalization;
    public class Printer: StreamWriter {
        public override IFormatProvider FormatProvider { get { return CultureInfo.InvariantCulture; } }
        public Printer(Stream stream) : base(stream, new UTF8Encoding(false, true)) { }
    }
    public class StreamScanner {
        public StreamScanner(Stream stream) { str = stream; }
        public readonly Stream str;
        private readonly byte[] buf = new byte[1024];
        private int len, ptr;
        public bool isEof = false;
        public bool IsEndOfStream { get { return isEof; } }
        private byte read() {
            if (isEof) return 0;
            if (ptr >= len) { ptr = 0; if ((len = str.Read(buf, 0, 1024)) <= 0) { isEof = true; return 0; } }
            return buf[ptr++];
        }
        public char Char() { byte b = 0; do b = read(); while ((b < 33 || 126 < b) && !isEof); return (char)b; }

        public string Scan() {
            var sb = new StringBuilder();
            for (var b = Char(); b >= 33 && b <= 126; b = (char)read())
                sb.Append(b);
            return sb.ToString();
        }
        public string ScanLine() {
            var sb = new StringBuilder();
            for (var b = Char(); b != '\n' && b != 0; b = (char)read())
                if (b != '\r') sb.Append(b);
            return sb.ToString();
        }
        public long Long() { return isEof ? long.MinValue : long.Parse(Scan()); }
        public int Integer() { return isEof ? int.MinValue : int.Parse(Scan()); }
        public double Double() { return isEof ? double.NaN : double.Parse(Scan(), CultureInfo.InvariantCulture); }
    }
}
#endregion


Measured memory_bytes: 13960