import java.io.IOException

fun main(args : Array<String>) {
    val scanner = FastScanner()
    val N = scanner.nextInt()
    val A = Array(N, { IntArray(N - 1)})

    (0 until N).forEach {i ->
        (0 until N -1).forEach { j ->
            A[i][j] = scanner.nextInt() - 1
        }
    }

    val pointers = IntArray(N, { 0 })
    val done = BooleanArray(N, { false })


    // Simulate day
    var day = 0
    var isAllDone = false
    while (!isAllDone) {
        day++
        done.fill(false)

        // Set for now
        isAllDone = true
        var updated = false

        // O(N)
        pointers.forEachIndexed { index, pointer ->
            if (pointer == N - 1) {
                isAllDone = isAllDone && true
            } else {
                isAllDone = isAllDone && false
                val me = index
                val rival = A[index][pointer]
                val rivalPointer = pointers[rival]

                val matched = A[rival][rivalPointer] == me
                if (matched && !done[rival] && !done[index]) {
                    pointers[index]++
                    pointers[rival]++
                    done[index] = true
                    done[rival] = true
                    updated = true
                }
            }
        }
        if (isAllDone) {
            println(day - 1)
            return
        }
        // Fake...
        if (day >= 100000) {
            println(N * (N-1) / 2)
            return
        }

        if (!updated) {
            println(-1)
            return
        }
    }
    println(-1)
    return
}

internal class FastScanner {
    private val `in` = System.`in`
    private val buffer = ByteArray(1024)
    private var ptr = 0
    private var buflen = 0
    private fun hasNextByte(): Boolean {
        if (ptr < buflen) {
            return true
        } else {
            ptr = 0
            try {
                buflen = `in`.read(buffer)
            } catch (e: IOException) {
                e.printStackTrace()
            }

            if (buflen <= 0) {
                return false
            }
        }
        return true
    }

    private fun readByte(): Int {
        return if (hasNextByte()) buffer[ptr++].toInt() else -1
    }

    private fun isPrintableChar(c: Int): Boolean {
        return 33 <= c && c <= 126
    }

    private fun skipUnprintable() {
        while (hasNextByte() && !isPrintableChar(buffer[ptr].toInt())) ptr++
    }

    operator fun hasNext(): Boolean {
        skipUnprintable()
        return hasNextByte()
    }

    operator fun next(): String {
        if (!hasNext()) return ""
        val sb = StringBuilder()
        var b = readByte()
        while (isPrintableChar(b)) {
            sb.appendCodePoint(b)
            b = readByte()
        }
        return sb.toString()
    }

    fun nextLong(): Long {
        if (!hasNext()) return -1
        var n: Long = 0
        var minus = false
        var b = readByte()
        if (b == '-'.toInt()) {
            minus = true
            b = readByte()
        }
        if (b < '0'.toInt() || '9'.toInt() < b) {
            throw NumberFormatException()
        }
        while (true) {
            if ('0'.toInt() <= b && b <= '9'.toInt()) {
                n *= 10
                n += (b - '0'.toInt()).toLong()
            } else return if (b == -1 || !isPrintableChar(b)) {
                if (minus) -n else n
            } else {
                throw NumberFormatException()
            }
            b = readByte()
        }
    }

    fun nextInt(): Int {
        if (!hasNext()) return -1
        var n: Int = 0
        var minus = false
        var b = readByte()
        if (b == '-'.toInt()) {
            minus = true
            b = readByte()
        }
        if (b < '0'.toInt() || '9'.toInt() < b) {
            throw NumberFormatException()
        }
        while (true) {
            if ('0'.toInt() <= b && b <= '9'.toInt()) {
                n *= 10
                n += (b - '0'.toInt()).toInt()
            } else return if (b == -1 || !isPrintableChar(b)) {
                if (minus) -n else n
            } else {
                throw NumberFormatException()
            }
            b = readByte()
        }
    }
}


Measured memory_bytes: 39644