#include<bits/stdc++.h>

using namespace std;

#define all(v)				((v).begin()), ((v).end())
#define allr(v)				((v).rbegin()), ((v).rend())
#define sz(v)				((int)((v).size()))
#define rep(i, v)		for(int i=0;i<sz(v);++i)
#define lp(i, n)		for(int i=0;i<(int)(n);++i)
#define lpi(i, j, n)	for(int i=(j);i<(int)(n);++i)
#define lpd(i, j, n)	for(int i=(j);i>=(int)(n);--i)
#define ll long long
#define pb					push_back
#define fIO ios_base::sync_with_stdio(0);cin.tie(0);

const ll oo = 1e8;
const double pi = 3.1415926535897;


const double EPS = (1e-7);
int dcmp(double x, double y) {	return fabs(x-y) <= EPS ? 0 : x < y ? -1 : 1;	}


typedef vector<int>                vi;
typedef vector<pair<int,int>>      vii;
typedef vector<ll>                 vll;
typedef vector<double>             vd;
typedef vector< vi >               vvi;
typedef vector< vd >               vvd;
typedef vector<string>             vs;
typedef pair<int, int>             pii;

/**
    * PLEASEEE READDD PROBLEEEM CARFULLY ****
    * Always check for OVERFLOW ll vs int
    * Always check for array bounds
    * Check for function return
    * READ OUTPUT SECTION AGAIN!!!
**/

struct edge{
    int from, to, w;

    edge(){}
    edge(int x, int y, int we): from(x), to(y), w(we){}

    bool operator < (const edge &rhs) const{
        return w > rhs.w;
    }

};

int main(){
    fIO

    int n, m;
    cin >> n >> m;

    int num[n] = {-1};

    for(int i = 0; i < m; i++) {
        int s, c;
        cin >> s >> c;

        if(num[s - 1] == -1) num[s - 1] = c;
        else if(num[s - 1] != c) return cout << -1, 0;
    }

    for(int i = 0; i < n; i++) {
        if(!i) {
            if(num[i] == -1) num[i] = 1;
            else if(num[i] == 0) return cout << -1, 0;
        }
    }

    for(int i = 0; i < n; i++) cout << max(0, num[i]);
}






