import std.stdio, std.string, std.conv, std.range;
import std.algorithm, std.array, std.typecons, std.container;
import std.math, std.numeric, std.random, core.bitop;

enum inf = 1_001_001_001;
enum infl = 1_001_001_001_001_001_001L;


void main() {
    int N, M;
    scan(N, M);
    auto a = new int[](N);
    a[] = -1;
    foreach (i ; 0 .. M) {
        int si, ci;
        scan(si, ci);
        si--;
        if (a[si] != -1 && a[si] != ci) {
            writeln(-1);
            return;
        }
        a[si] = ci;
    }
    if (a[0] == 0) {
        writeln(-1);
        return;
    }
    foreach (i ; 0 .. N) {
        if (a[i] != -1) {
            write(a[i]);
        }
        else {
            write(i == 0 ? 1 : 0);
        }
    }
    writeln;
}




void scan(T...)(ref T args) {
    auto line = readln.split;
    foreach (ref arg; args) {
        arg = line.front.to!(typeof(arg));
        line.popFront;
    }
    assert(line.empty);
}

void fillAll(R, T)(ref R arr, T value) {
    static if (is(typeof(arr[] = value))) {
        arr[] = value;
    }
    else {
        foreach (ref e; arr) {
            fillAll(e, value);
        }
    }
}

bool chmin(T, U...)(ref T x, U args) {
    bool isChanged;
    foreach (arg; args) if (x > arg) {
        x = arg;
        isChanged = true;
    }
    return isChanged;
}

bool chmax(T, U...)(ref T x, U args) {
    bool isChanged;
    foreach (arg; args) if (x < arg) {
        x = arg;
        isChanged = true;
    }
    return isChanged;
}



