import core.bitop, std.algorithm, std.ascii, std.bigint, std.conv, std.math,
    std.functional, std.numeric, std.range, std.stdio, std.string, std.random,
    std.typecons, std.container, std.format;

// dfmt off
T lread(T = long)(){return readln.chomp.to!T();}
T[] aryread(T = long)(){return readln.split.to!(T[])();}
void scan(TList...)(ref TList Args){auto line = readln.split();
foreach (i, T; TList){T val = line[i].to!(T);Args[i] = val;}}
alias sread = () => readln.chomp();enum MOD = 10 ^^ 9 + 7;
alias PQueue(T, alias less = "a<b") = BinaryHeap!(Array!T, less);
// dfmt on

void main()
{
    long N, M;
    scan(N, M);
    auto ans = new long[](N);
    ans[] = -1;
    foreach (_; 0 .. M)
    {
        long S, C;
        scan(S, C);
        if (ans[S - 1] != -1 && ans[S - 1] != C)
        {
            writeln(-1);
            return;
        }
        ans[S - 1] = C;
    }
    if (ans[0] == 0)
    {
        writeln(-1);
        return;
    }
    ans[0] = max(ans[0], 1);
    foreach (i; 1 .. N)
        if (ans[i] == -1)
        {
            ans[i] = 0;
        }
    ans.map!text().join().writeln();
}
