//#include <bits/stdc++.h>
#include "bits/stdc++.h"
#define rep(i, n) for (int i = 0; i < (n); ++i)
using namespace std;
typedef long long ll;
typedef pair<int, int> P;
typedef vector<int> VI;
typedef vector<VI> VVI;//例: VVI dp(10, vector<int>(10, INF);
typedef priority_queue<int, vector<int>, less<int> > QUE_int;
const int INF = 2 * pow(10, 9) + 1;//+1しないとREになるかも(out of rangeになるんかな?? )

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

ll max(ll a, ll b) { return (a > b) ? a : b; }
ll min(ll a, ll b) { return (a < b) ? a : b; }

////////////////////////////////////////////////////////////////

// auto mod int
// https://youtu.be/L8grWxBlIZ4?t=9858
// https://youtu.be/ERZuLAxZffQ?t=4807 : optimize
// https://youtu.be/8uowVvQ_-Mo?t=1329 : division
const int mod = pow(10, 9) + 7;
struct mint {
	ll x; // typedef long long ll;
	mint(ll x = 0) :x((x%mod + mod) % mod) {}
	mint operator-() const { return mint(-x); }
	mint& operator+=(const mint a) {
		if ((x += a.x) >= mod) x -= mod;
		return *this;
	}
	mint& operator-=(const mint a) {
		if ((x += mod - a.x) >= mod) x -= mod;
		return *this;
	}
	mint& operator*=(const mint a) {
		(x *= a.x) %= mod;
		return *this;
	}
	mint operator+(const mint a) const {
		mint res(*this);
		return res += a;
	}
	mint operator-(const mint a) const {
		mint res(*this);
		return res -= a;
	}
	mint operator*(const mint a) const {
		mint res(*this);
		return res *= a;
	}
	mint pow(ll t) const {
		if (!t) return 1;
		mint a = pow(t >> 1);
		a *= a;
		if (t & 1) a *= *this;
		return a;
	}

	// for prime mod
	mint inv() const {
		return pow(mod - 2);
	}
	mint& operator/=(const mint a) {
		return (*this) *= a.inv();
	}
	mint operator/(const mint a) const {
		mint res(*this);
		return res /= a;
	}
};
// combination mod prime
// https://www.youtube.com/watch?v=8uowVvQ_-Mo&feature=youtu.be&t=1619
struct combination {
	vector<mint> fact, ifact;
	combination(int n) :fact(n + 1), ifact(n + 1) {
		assert(n < mod);
		fact[0] = 1;
		for (int i = 1; i <= n; ++i) fact[i] = fact[i - 1] * i;
		ifact[n] = fact[n].inv();
		for (int i = n; i >= 1; --i) ifact[i - 1] = ifact[i] * i;
	}
	mint operator()(int n, int k) {
		if (k < 0 || k > n) return 0;
		return fact[n] * ifact[k] * ifact[n - k];
	}
};


////////////////////////////////////////////////////////////////

int main(void) {
	int N, M;
	cin >> N >> M;
	vector<int> s(M), c(M);
	for (int i = 0; i < M; i++) {
		int s_tmp, c_tmp;
		cin >> s_tmp >> c_tmp;
		s_tmp--;
		s[i] = s_tmp;
		c[i] = c_tmp;
	}
	bool ans = true;

	if (N != 1) {
		for (int i = 0; i < M; i++) {//Nが2以上で　かつ　左から1桁目が0であるならfalse
			if (s[i] == 0 && c[i] == 0) ans = false;
		}
	}

	vector<int> num(3, -1);//num[i]:左からi桁目の数字 (0 ～ 9)

	for (int i = 0; i < M; i++) {
		if (num[s[i]] == -1) num[s[i]] = c[i];
		else {//左からs[i]桁目に既に数字が入っているなら...
			if (num[s[i]] == c[i]);//既に入っている数字と一致していたら無視
			else ans = false;
		}
	}

	if (ans == false) {
		cout << "-1" << endl;
		return 0;
	}

	if (N != 1) {
		if(num[0] == -1) num[0] = 1;
	}
	else {//N==1なら
		if (num[0] == -1) num[0] = 0;
	}

	if (N >= 2) {
		if (num[1] == -1) num[1] = 0;
	}
	if (N == 3) {
		if (num[2] == -1) num[2] = 0;
	}

	

	if (N == 1) {
		cout << num[0] << endl;
	}
	else if (N == 2) {
		cout << num[0] << num[1] << endl;
	}

	else {
		cout << num[0] << num[1] << num[2] << endl;
	}
}




Measured memory_bytes: 256