// 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 ans = new long[](N);
    ans[0] = 1;
    auto visited = new long[](N);
    visited[] = -1;
    foreach (_; 0 .. M)
    {
        long s, c;
        scan(s, c);
        s--;
        if (visited[s] != -1 && visited[s] != c)
        {
            writeln(-1);
            return;
        }
        if (N != 1 && s == 0 && c == 0)
        {
            writeln(-1);
            return;
        }
        visited[s] = c;
        ans[s] = c;
    }
    ans.map!"cast(char)(a+'0')"().array.writeln();
}
