#include <bits/stdc++.h>
using namespace std;

#define rep(i,n) for(int i=0;i<n;i++)
#define REP(i,s,n) for(int i=(s);i<(n);i++)
#define repr(i,n) for(int i=n-1;i>=0;i--)
#define REPR(i,s,n) for(int i=(s);i>=(n);i--)
#define all(a) (a).begin(),(a).end()
#define rall(a) (a).rbegin(),(a).rend()
#define Eunique(v) v.erase(unique(all(v)),v.end())
#define Eback(s) s.erase(s.end()-1,s.end())
#define rev(v) reverse(all(v))
#define pb push_back
#define pf push_front
#define mod 1000000007
#define m_p make_pair
#define DOUBLE fixed << setprecision(15)
#define OK puts("OK")
#define OK1 puts("OK1")
#define OK2 puts("OK2")
#define SIZE(s) (int)s.size()
#define INF ((1LL<<62)-(1LL<<31))

typedef vector<int> vi;
typedef vector<vi> vvi;
typedef vector<double> vd;
typedef long long ll;
typedef vector<ll> vll;
typedef vector<vll> vvll;
typedef pair<ll,ll> pll;
typedef pair<int,int> pii;
typedef vector<pair<int,int>> vpii;
typedef vector<pair<ll,ll>> vpll;
typedef vector<string> vs;
const double pi = acos(-1.0);

template<class A, class B>
ostream& operator<<(ostream& ost, const pair<A, B>&p) {
	ost << "{" << p.first << ", " << p.second << "} ";
	return ost;
}

template<class T>
ostream& operator<<(ostream& ost, const vector<T>&v) {
	ost << "{";
	for (int i = 0; i<(int)v.size(); i++) {
		if (i)ost << " ";
		ost << v[i];
	}
	ost << "} \n";
	return ost;
}

template<class A, class B>
ostream& operator<<(ostream& ost, const map<A, B>&v) {
	ost << "{";
	for (auto p:v) {
		ost << "{" << p.first << ", " << p.second << "} ";
	}
	ost << "} ";
	return ost;
}

template<class T>
inline bool chmax(T& a, T b){if(a<b){a=b;return true;} return false;}

template<class T>
inline bool chmin(T& a, T b){if(a>b){a=b;return true;} return false;}

ll gcd(ll x, ll y) {return __gcd(x,y);}
ll lcm(ll x, ll y) {return x/__gcd(x,y)*y;}

int main()
{
	ll n,m;
	cin >> n >> m;
	vpll v(m);
	rep(i,m) cin >> v[i].first >> v[i].second;
	sort(all(v));
	//cout << v << endl;
	rep(i,m-1){
		if(v[i].first==v[i+1].first&&v[i].second!=v[i+1].second){
			cout << -1 << endl;
			return 0;
		}
	}
	Eunique(v);
	vll a(10,-1);
	rep(i,SIZE(v)) a[v[i].first]=v[i].second;
	//cout << v << endl;
	//cout << a << endl;
	string s="";
	rep(i,n){
		if(a[i+1]!=-1) s+=to_string(a[i+1]);
		else s+="1";
	}
	if(SIZE(s)==2&&s[0]=='0') cout << -1 << endl;
	else if(SIZE(s)==3&&s[0]=='0') cout << -1 << endl;
	else cout << s << endl;
	return 0;
}