import kotlin.math.min

fun main() = agc039b()

@OptIn(ExperimentalStdlibApi::class)
fun agc039b() = IO_agc039b().exec {
    val n = readInt()
    val sList = Array(n) { readString().map { it == '1' }.toBooleanArray() }

    val uf = UnionFind(n * 2)

    for (u in 0 until n) for (v in u + 1 until n) {
        if (sList[u][v]) uf.apply { unite(u, v + n); unite(u + n, v) }
    }

    for (i in 0 until n) if (uf.isSame(i, i + n)) return@exec println(-1)

    val dist = Array(n) { i -> IntArray(n) { if (it == i) 0 else Int.MAX_VALUE / 1000 } }

    for (u in 0 until n) for (v in u + 1 until n) {
        if (sList[u][v]) {
            dist[u][v] = 1
            dist[v][u] = 1
        }
    }

    for (k in 0 until n) for (i in 0 until n) for (j in 0 until n) {
        dist[i][j] = min(dist[i][j], dist[i][k] + dist[k][j])
    }

    val answer = dist.map { it.max()!! }.max()!! + 1

    println(answer)
}

private class UnionFind(initSize: Int) {
    private val parent = IntArray(initSize) { it }
    private val size = LongArray(initSize) { 1L }

    fun root(x: Int): Int {
        if (x == parent[x]) return x

        val xr = root(parent[x])
        parent[x] = xr
        return xr
    }

    fun unite(x: Int, y: Int) {
        val xr = root(x)
        val yr = root(y)
        if (xr == yr) return

        if (size[xr] >= size[yr]) {
            size[xr] += size[yr]
            parent[yr] = xr
        } else {
            size[yr] += size[xr]
            parent[xr] = yr
        }
    }

    fun isSame(x: Int, y: Int): Boolean = root(x) == root(y)

    fun unite(pair: Pair<Int, Int>): Unit = unite(pair.first, pair.second)
    fun isSame(pair: Pair<Int, Int>): Boolean = isSame(pair.first, pair.second)

    fun size(x: Int): Long = size[root(x)]
}

// region kokokara template dayo (^o^)
@Suppress("unused", "ClassName", "SpellCheckingInspection", "ConvertToStringTemplate", "MemberVisibilityCanBePrivate")
private class IO_agc039b(private val separator: String = System.lineSeparator()) {
    private val input = System.`in`
    private val buffer = ByteArray(1024)
    private var pointer = 0
    private var bufferLength = 0
    private val sb = StringBuilder()
    private fun Byte.isPrintable() = this in 33..126
    private fun Byte.isNumeric() = this in '0'.toByte()..'9'.toByte()
    private fun Byte.toNumVal() = if (this.isNumeric()) this - '0'.toByte() else error("$this is not numeric")

    private fun hasNextByte(): Boolean {
        return if (pointer < bufferLength) true else {
            pointer = 0
            bufferLength = input.read(buffer)
            bufferLength > 0
        }
    }

    private fun readByte(): Byte = if (hasNextByte()) buffer[pointer++] else -1
    private fun skipUnprintable() = run { while (hasNextByte() && !buffer[pointer].isPrintable()) pointer++ }
    private fun hasNext(): Boolean = run { skipUnprintable() }.run { hasNextByte() }
    private fun hasNextOrError() = if (!hasNext()) error("has no next element.") else Unit

    fun readString(): String {
        hasNextOrError()
        val sb = StringBuilder()
        var b = readByte()
        while (b.isPrintable()) {
            sb.appendCodePoint(b.toInt())
            b = readByte()
        }
        return sb.toString()
    }

    fun readLong(): Long {
        hasNextOrError()
        var n = 0L
        var negative = false
        var b = readByte()
        if (b == '-'.toByte()) {
            negative = true
            b = readByte()
        }
        if (!b.isNumeric()) error("$b is not numeric.")
        while (true) {
            when {
                b.isNumeric() -> n = n * 10 + b.toNumVal()
                b.toInt() == -1 || !b.isPrintable() -> return if (negative) -n else n
                else -> error("failed to parse. [n=$n, b=$b]")
            }
            b = readByte()
        }
    }

    fun readInt() = readLong()
        .let { if (it in Int.MIN_VALUE..Int.MAX_VALUE) it.toInt() else error("$it is not in range of Int.") }

    fun readDouble(): Double {
        var n = 0.0
        var div = 1.0
        var negative = false
        var b = readByte()
        if (b == '-'.toByte()) {
            negative = true
            b = readByte()
        }
        do n = n * 10 + b.toNumVal()
        while (run { b = readByte() }.run { b.isNumeric() })
        if (b == '.'.toByte()) {
            while (run { b = readByte() }.run { b.isNumeric() })
                n += b.toNumVal() / (run { div *= 10 }.run { div })
        }
        return if (negative) -n else n
    }

    fun println(): Unit = run { sb.append(separator) }
    fun print(any: Any): Unit = run { sb.append(any) }
    fun println(any: Any): Unit = run { sb.append(any.toString() + separator) }
    fun flush() = run { kotlin.io.println(sb); sb.clear() }

    fun exec(action: IO_agc039b.() -> Unit) {
        var t: Throwable? = null
        Thread(null, { action() }, "solve", 128 * 1024 * 1024)
            .apply { setUncaughtExceptionHandler { _, t1 -> t = t1 } }
            .apply { start() }.join()
        t?.let { throw it }
        kotlin.io.print(sb)
    }

    fun readLine(): Nothing = error("readLine is disabled.")
}
// endregion kokomade template dayo (^o^)


Measured memory_bytes: 40292