#include <bits/stdc++.h>
using namespace std;
long long day[12] = {31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
long long dx[] = {0, 1, 0, -1};
long long dy[] = {1, 0, -1, 0};
const long long MOD = 1000000007LL;
bool isupper(char c) {
  if ('A' <= c && c <= 'Z') return 1;
  return 0;
}
bool islower(char c) {
  if ('a' <= c && c <= 'z') return 1;
  return 0;
}
bool isnumber(char c) { return ('0' <= c && c <= '9'); }
bool isalpha(char c) { return (isupper(c) || islower(c)); }
bool is_kaibun(string s) {
  string rs = s;
  reverse((rs).begin(), (rs).end());
  if (s == rs)
    return true;
  else
    return false;
}
template <typename T>
void print(vector<T> v) {
  for (long long i = 0; i < v.size(); i++) {
    if (i) cout << " ";
    cout << v[i];
  }
  cout << endl;
}
long long INF = 1e18;
template <typename T>
void printendl(vector<T> v) {
  for (auto date : v) cout << date << endl;
}
template <typename T>
void printvv(vector<vector<T>> v) {
  for (long long i = 0; i < v.size(); i++) {
    for (long long j = 0; j < v[i].size(); j++) {
      if (j) cout << " ";
      cout << v[i][j];
    }
    cout << endl;
  }
}
struct Point {
  long long x, y, num;
  double e_dis(Point other) {
    return sqrt((x - other.x) * (x - other.x) + (y - other.y) * (y - other.y));
  }
};
long long gcd(long long a, long long b) {
  if (b == 0)
    return a;
  else
    return gcd(b, a % b);
}
bool isPrime(long long x) {
  if (x == 1) return 0;
  if (x == 2) return 1;
  if (x % 2 == 0) return 0;
  for (long long i = 3; i * i <= x; i++)
    if (x % i == 0) return 0;
  return 1;
}
double f(long long p) {
  float ret = 0;
  for (long long i = (long long)0; i < (long long)p; i++) {
    ret += 1000000.0 / p * (i + 1);
  }
  return ret;
}
long long f(vector<long long> v, long long x) {
  long long ret = 0;
  for (long long i = (long long)0; i < (long long)v.size(); i++) {
    ret += (v[i] - x) * (v[i] - x);
  }
  return ret;
}
signed main() {
  long long n, m;
  cin >> n >> m;
  map<long long, long long> mp;
  for (long long i = (long long)0; i < (long long)m; i++) {
    long long s, c;
    cin >> s >> c;
    if (mp[s] != 0 && mp[s] != c) {
      cout << "-1" << endl;
      return 0;
    }
    if (s == 1 && c == 0) {
      cout << -1 << endl;
      return 0;
    }
    mp[s] = c;
  }
  vector<long long> ans = vector<long long>(n, -1);
  for (auto x : mp) {
    ans[x.first - 1] = x.second;
  }
  for (long long i = (long long)1; i < (long long)ans.size(); i++) {
    if (ans[i] == -1) ans[i] = 0;
  }
  if (ans[0] == -1) ans[0] = 1;
  for (long long i = (long long)0; i < (long long)ans.size(); i++) {
    cout << ans[i];
  }
  cout << endl;
}
