// dfmt off
T lread(T=long)(){return readln.chomp.to!T;}T[] lreads(T=long)(long n){return iota(n).map!((_)=>lread!T).array;}
T[] aryread(T=long)(){return readln.split.to!(T[]);}void arywrite(T)(T a){a.map!text.join(' ').writeln;}
void scan(L...)(ref L A){auto l=readln.split;foreach(i,T;L){A[i]=l[i].to!T;}}alias sread=()=>readln.chomp();
void dprint(L...)(lazy L A){debug{auto l=new string[](L.length);static foreach(i,a;A)l[i]=a.text;arywrite(l);}}
static immutable MOD=10^^9+7;alias PQueue(T,alias l="b<a")=BinaryHeap!(Array!T,l);import std, core.bitop;
// dfmt on

void main()
{
    long N, M;
    scan(N, M);

    auto S = new long[](M);
    auto C = new long[](M);
    foreach (i; 0 .. M)
    {
        scan(S[i], C[i]);
        S[i]--;
    }

    x: foreach (x; 0 .. 1000)
    {
        auto s = x.to!string;
        if (s.length != N)
            continue x;
        foreach (i; 0 .. M)
        {
            if (s[S[i]] != C[i] + '0')
            {
                continue x;
            }
        }
        writeln(x);
        return;
    }
    writeln(-1);
}
