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

#define int long long
#define vvi vector<vector<int>>
#define vec vector
#define pq priority_queue
#define all(v) (v).begin(), (v).end()
#define uniqueV(x) sort(x.begin(), x.end()); x.erase(unique(x.begin(), x.end()), x.end());
#define rep(i, n) for (int (i) = (0); (i) < (n); ++(i))
#define repp(i, m, n) for (int (i) = (m); (i) < (n); ++(i))
#define dbg(x) cerr << #x << ": " << x << endl;
#define dbg2(x, y) cerr<<"("<<#x<<", "<<#y<<") = "<<"("<<x<<", "<<y<<")"<<endl;
#define dbg3(x, y, z) cerr<<"("<<#x<<", "<<#y<<", "<<#z<<") = "<<"("<<x<<", "<<y<<", "<<z<<")"<<endl;
#define dbgB(value, size) cerr<<#value<<": "<<bitset<size>(value) << endl;
#define line() cerr << "---------------" << endl;

const int dx[] = {1, -1, 0, 0};
const int dy[] = {0, 0, -1, 1};
const double PI = 3.14159265358979323846;

template<class T>bool chmax(T &a, const T &b) { if (a<b) { a = b; return 1; } return 0; }
template<class T>bool chmin(T &a, const T &b) { if (b<a) { a = b; return 1; } return 0; }

template<typename T>
void print1(T begin, T end) {
	while (begin != end) {
		cerr << (*begin) << " ";
		*begin++;
	}
	cerr << endl;
}

template<typename T>
void print2(T Array, int height, int width) {
	for (int i = 0; i < height; i++) {
		for (int j = 0; j < width; j++) {
			cerr << " " << Array[i][j];
		}
		cerr << endl;
	}
}

void print() { std::cerr << endl; }
template <class Head, class... Tail>
void print(Head&& head, Tail&&... tail) {
	std::cerr << head << " ";
	print(std::forward<Tail>(tail)...);
}

template<class T>
void Add(T &a, const T &b, const T &mod=1000000007) {
	int val = ((a % mod) + (b % mod)) % mod;
	if (val < 0) { val += mod; }
	a = val;
}

template <typename X, typename T> auto vectors(X x, T a) { return vector<T>(x, a); }
template <typename X, typename Y, typename Z, typename... Zs> auto vectors(X x, Y y, Z z, Zs... zs) { auto cont = vectors(y, z, zs...); return vector<decltype(cont)>(x, cont); }

// ------------------------------------------------------------------------------------------

int N, M;
int s[10];
int c[10];
vector<int> ans;

// 先頭の0
// s, cの条件
bool check(vector<int> v) {
	if (v[0] == 0) {
		return false;
	}

	rep (i, M) {
		if (v[s[i]-1] != c[i]) {
			return false;
		}
	}

	return true;
}

// vectorを数値に変換
int trans(vector<int> v) {
	int ten = 1;
	int num = 0;
	for (int i = N - 1; i >= 0; i--) {
		num += v[i] * ten;
		ten *= 10;
	}

	return num;
}

void dfs(int idx, vector<int> v) {
	if (idx >= N) {
		if (check(v)) {
			ans.push_back(trans(v));
		}
		return;
	} else {
		for (int i = 0; i <= 9; i++) {
			v.push_back(i);
			dfs(idx + 1, v);
			v.pop_back();
		}
	}
}

signed main() {
	cin >> N >> M;
	rep (i, M) {
		cin >> s[i] >> c[i];
	}

	vector<int> t;
	dfs(0, t);

	if (ans.size() == 0) {
		cout << -1 << endl;
	} else {
		sort(all(ans));
		cout << ans[0] << endl;
	}

	return 0;
}