/******************************************
* AUTHOR : RAJAGOPALAN *
* NICK : ARNO *
* INSTITUTION : VIT *
******************************************/
#include <bits/stdc++.h>
#include <ext/pb_ds/detail/standard_policies.hpp>
#define ll long long
#define ull unsigned long long
#define pb push_back
#define mp make_pair
#define all(x) (x).begin(),(x).end()
#define alli(a, n, k) (a+k),(a+n+k)
#define FP(i, a, b, k) for(__typeof(a) i = a;i < b;i += k)
#define FS(i, a, b, k) for(__typeof(a) i = a;i > b;i -= k)
#define IT(it, a) for(__typeof(a.begin()) it = a.begin();it != a.end(); ++it)
#define ordered_set tree<int, null_type, less<int>, rb_tree_tag, tree_order_statistics_node_update>
#define eps 1e-6
#define pi 3.141592653589793
using namespace std;
using namespace __gnu_pbds;

template<class T> inline T gcd(T x, T y) { if (!y) return x; return gcd(y, x%y);}
typedef vector<int> VII;
typedef vector<ll> VLL;
typedef pair<int, int> PII;
typedef vector< pair<int, int> > VPII;
typedef vector< pair<int, PII > > VPPI;
const int MOD = 1e9 + 7;
const int INF = 1e9;

inline ll modulo(ll a, ll m)
{
	return (a % m + m) % m;
}

inline ll modInverse(ll a, ll m)
{
	assert(__gcd(a, m) == 1);
	ll m0 = m;
	ll y = 0, x = 1;

	if (m == 1)
		return 0;

	while (a > 1)
	{
		ll q = a / m;
		ll t = m;

		m = a % m, a = t;
		t = y;

		y = x - q * y;
		x = t;
	}

	if (x < 0)
		x += m0;

	return x;
}

inline ll modPow(ll x, ll y, ll m)
{ //x^y % m
	if (y == 0)
		return 1LL;
	else if (y == 1)
		return x;
	else
	{
		ll ans = modPow(x, y / 2, m) % m;
		if (y & 1)
		{
			return (((ans * ans) % m) * x) % m;
		}
		else
		{
			return (ans * ans) % m;
		}
	}
}

int main(int argc, char* argv[])
{
	ios::sync_with_stdio(false);
	cin.tie(NULL);
	int n,m;
	cin>>n>>m;
	VII num(n,-1);
	bool win=true;
	while(m--)
	{
		int g,v;
		cin>>g>>v;
		g--;
		if(num[g]==-1)
		num[g]=v;
		else if(num[g]!=v)
		win=false;
		
	}
	//cout<<win<<endl;
	if(num[0]==0 && n!=1)win=false;
	else if(num[0]==-1)num[0]=1;
	for(int i=1;i<n;++i)
	if(num[i]==-1)num[i]=0;

	if(win)
	{
		for(auto x:num)cout<<x;
	}
	else cout<<-1;

	return 0;
}