fun main() {
    val (n, m) = readInts()
    val s = List(n) { readln() }
    println((0 until m).map { p ->
        val count = IntArray(26)
        for (l in s) {
            count[l[p] - 'a']++
        }
        (count.indices.maxBy { count[it] } + 'a'.code).toChar()
    }.joinToString(""))
}

private fun readInts() = readln().split(" ").map { it.toInt() }