import java.util.*
import java.math.*

fun main(args: Array<String>) {

    var (H, W) = readLine()!!.split(" ").map { it.toInt() }
//    var N = readLine()!!.toLong()
//    val S = readLine()!!
//    val D = readLine()!!.split(" ").map { it.toLong() }
    val S = Array(H){readLine()!!}
    val mod = 1000000007L

    var lightH = IntArray(W)

    var ans = 0

    for ((h,s) in S.withIndex()) {
        var lightW = 0
        for ((w , c) in s.withIndex()) {
            if (c == '#') {
                lightH[w] = 0
                lightW = 0
                continue
            }
            if (lightH[w] == 0) {
                var count = 0
                for (i in h until H) {
                    if (S[i][w] == '#') break
                    count++
                }
                lightH[w] = count
            }
            if (lightW == 0) {
                var count = 0
                for (i in w until W) {
                    if (s[i] == '#') break
                    count++
                }
                lightW = count
            }
//            println ("$h $w ${lightH[w]} ${lightW}")
            ans = Math.max(ans, lightW+lightH[w]-1)
        }
    }

    println(ans)
}