package sprint6.fin.B

import java.io.BufferedReader
import java.io.InputStreamReader
import java.util.*

fun main() {
    val buffer = BufferedReader(InputStreamReader(System.`in`))
    val cityCount = buffer.readLine().toInt()
    val graph = buildMap<Int, Visited> {
        (1..cityCount).forEach { put(it, Visited(Color.WHITE, mutableSetOf())) }
        repeat(cityCount - 1) {
            val cityId = it + 1
            buffer.readLine().forEachIndexed { index, way ->
                val toCity = index + cityId + 1
                when (way) {
                    'R' -> this[cityId]!!.edges.add(toCity)
                    'B' -> this[toCity]!!.edges.add(cityId)
                }
            }
        }
    }

    for (next in graph.entries) {
        if (next.value.color != Color.WHITE) continue

        val stack = Stack<Int>()
        stack.add(next.key)

        while (!stack.empty()) {
            val cur = stack.pop()
            val curVisited = graph[cur]!!
            if (curVisited.color == Color.WHITE) {
                curVisited.color = Color.GREY
                stack.push(cur)
                curVisited.edges.forEach {
                    val color = graph[it]!!.color
                    if (color == Color.WHITE)
                        stack.push(it)
                    if (color == Color.GREY) {
                        println("NO")
                        return
                    }
                }
            } else if (curVisited.color == Color.GREY) {
                curVisited.color = Color.BLACK
            }
        }
    }
    if (graph[cityCount]!!.color == Color.BLACK)
        println("YES")
    else println("NO")
}

data class Visited(var color: Color, val edges: MutableSet<Int>)

enum class Color {
    WHITE,
    GREY,
    BLACK
}