#include <iostream>
#include <vector>
#include <algorithm>
#include <map>
#include <string>
#include <queue>
#include <fstream>
#include <string>
#include <math.h>
#include <set>
#include <string>
#include <bitset>
#include <fstream>
#include <stack>
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
typedef pair<ll, ll> P;
typedef pair<ll, P> T;

#define rep(i, n) for (ll i = 0; i < (n); i++)
#define revrep(i, n) for (ll i = (n) - 1; i >= 0; i--)
#define f first
#define s second
#define pb push_back

ll mod = 1000000007;
const ll INF = 100000000000010000;
//const ull B = 998244353;
//ll kai[3010];

//void pres(double A, ll x = 20) { printf("%.20f\n", x); }

vector<ll> dx = { 0, 1, 0, -1, 1, -1, 1, -1, 0};
vector<ll> dy = { 1, 0, -1, 0, 1, 1, -1, -1, 0};

void chmin(ll& x, ll y) {
	x = min(x, y);
}

void chmax(ll& x, ll y) {
	x = max(x, y);
}

ll pow_long(ll x, ll y) {
	ll res = 1;
	while (y > 0) {
		if (y % 2 == 1) res *= x;
		x *= x;
		y /= 2;
	}
	return res;
}

void test() {
	cout << "888888888888888888888888" << endl;
}

ll gcd(ll x, ll y) {
	if (y == 0) return x;
	return gcd(y, x % y);
}

ll pow_mod(ll x, ll k) {
	x %= mod;
	ll res = 1;
	while (k > 0) {
		if (k % 2) {
			res *= x; res %= mod;
		}
		x *= x; x %= mod;
		k /= 2;
	}
	return res;
}

ll div_mod(ll x) {
	return pow_mod(x, mod - 2);
}

//コンビネーション
const int MAXcomb = 1000010;
ll fac[MAXcomb], finv[MAXcomb], inv[MAXcomb];
//facはn!,finvは1/n!
//invは逆元
void COMinit() {
	fac[0] = fac[1] = 1;
	finv[0] = finv[1] = 1;
	inv[1] = 1;
	for (int i = 2; i < MAXcomb; i++) {
		fac[i] = fac[i - 1] * i % mod;
		inv[i] = mod - inv[mod%i] * (mod / i) % mod;
		finv[i] = finv[i - 1] * inv[i] % mod;
	}
}
ll comb(int n, int k) {
	if (n < k) return 0;
	if (n < 0 || k < 0) return 0;
	return fac[n] * finv[k] % mod * finv[n - k] % mod;
}

ll N;
ll M;
ll s;
ll c;
ll ans[4];
bool jud = true;

void solve() {
	cin >> N >> M;
	rep(i, 4) ans[i] = -1;
	rep(i, M) {
		cin >> s >> c;
		if (ans[s] != -1 && ans[s] != c) {
			jud = false;
		}
		ans[s] = c;
	}
	if (!jud) {
		cout << -1 << endl;
		return;
	}
	if (ans[1] == 0) {
		cout << -1 << endl;
		return;
	}
	if (ans[1] == -1) ans[1] = 1;
	if (ans[2] == -1) ans[2] = 0;
	if (ans[3] == -1) ans[3] = 0;
	rep(i, N) cout << ans[i + 1];
	cout << endl;
}

int main() {
	cin.tie(0);
	ios::sync_with_stdio(false);
	ll T = 1;
	//cin >> T;
	rep(i, T) solve();
}
