import java.io.*
import java.lang.RuntimeException

val pw = PrintWriter(System.out)
const val MOD = 1000000007L
const val INF = 2147483647
const val LINF = 9223372036854775807L

fun main(args: Array<String>) {
    solve()
    pw.flush()
}

fun solve() {
    val (n, m) = nextIntList()
    val rule = intAry2(m, 2)
    repeat(m){
        val (s, c) = nextIntList()
        rule[it][0] = s - 1
        rule[it][1] = c
    }

    make(n, "")

    var ans = INF
    for(num in nums){
        if(num.first() == '0' && n > 1) continue
        var flag = false
        for(i in rule.indices){
            val keta = rule[i][0]
            if(num[keta].toString().toInt() != rule[i][1]){
                flag = true
                break
            }
        }
        if(flag) continue
        ans = min(ans, num.toInt())
    }

    println(if(ans == INF) -1 else ans)

}

val nums: MutableList<String> = mutableListOf()
fun make(n: Int, str: String){
    if(str.length == n){
        nums.add(str)
        return
    }
    for (i in 0..9){
        make(n, str + i.toString())
    }

}

fun println(v: String) {
    pw.println(v)
}

fun print(v: String) {
    pw.print(v)
}

fun next() = readLine()!!
fun nextInt() = next().toInt()
fun nextLong() = next().toLong()
fun nextDouble() = next().toDouble()
fun nextList() = next().split(" ").toMutableList()
fun nextIntList(index: Int = 0) = next().split(" ").map { it.toInt() + index }.toMutableList()
fun nextLongList(index: Long = 0L) = next().split(" ").map { it.toLong() + index }.toMutableList()
fun nextDoubleList() = next().split(" ").map { it.toDouble() }.toMutableList()

fun ary(n: Int, init: String = "") = Array(n) { init }
fun intAry(n: Int, init: Int = 0) = IntArray(n) { init }
fun longAry(n: Int, init: Long = 0L) = LongArray(n) { init }
fun doubleAry(n: Int, init: Double = 0.0) = DoubleArray(n) { init }
fun ary2(n: Int, m: Int, init: String = "") = Array(n) { Array(m) { init } }
fun intAry2(n: Int, m: Int, init: Int = 0) = Array(n) { IntArray(m) { init } }
fun longAry2(n: Int, m: Int, init: Long = 0) = Array(n) { LongArray(m) { init } }
fun doubleAry2(n: Int, m: Int, init: Double = 0.0) = Array(n) { DoubleArray(m) { init } }
fun ary3(n: Int, m: Int, k: Int, init: String = "") = Array(n) { Array(m) { Array(k) { init } } }
fun intAry3(n: Int, m: Int, k: Int, init: Int = 0) = Array(n) { Array(m) { IntArray(k) { init } } }
fun longAry3(n: Int, m: Int, k: Int, init: Long = 0L) = Array(n) { Array(m) { LongArray(k) { init } } }
fun doubleAry3(n: Int, m: Int, k: Int, init: Double = 0.0) = Array(n) { Array(m) { DoubleArray(k) { init } } }

fun abs(n: Int): Int = Math.abs(n)
fun abs(n: Long): Long = Math.abs(n)
fun abs(n: Double): Double = Math.abs(n)
fun max(vararg values: Int) = if (values.isEmpty()) -INF else values.max()!!
fun max(vararg values: Long) = if (values.isEmpty()) -LINF else values.max()!!
fun min(vararg values: Int) = if (values.isEmpty()) INF else values.min()!!
fun min(vararg values: Long) = if (values.isEmpty()) LINF else values.min()!!
fun swap(a: String, b: String) = Pair<String, String>(b, a)
fun swap(a: Int, b: Int) = Pair<Int, Int>(b, a)
fun swap(a: Long, b: Long) = Pair<Long, Long>(b, a)
fun swap(a: Double, b: Double) = Pair<Double, Double>(b, a)