fun main() {
    val (n, m) = readInts()
    val s = List(n) { readln() }
    println((0 until m).map { p ->
        s.map { it[p] }.groupingBy { it }.eachCount().entries.minWith(
            compareBy({ -it.value }, { it.key })
        ).key
    }.joinToString(""))
}

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