#include <bits/stdc++.h>
using namespace std;
const long long mod = 1000000007;
const long long INF = mod * mod;
const long double eps = 1e-12;
const long double pi = acos(-1.0);
long long mod_pow(long long a, long long n, long long m) {
  long long res = 1;
  while (n) {
    if (n & 1) res = res * a % m;
    a = a * a % m;
    n >>= 1;
  }
  return res;
}
struct modint {
  long long n;
  modint() : n(0) { ; }
  modint(long long m) : n(m) {
    if (n >= mod)
      n %= mod;
    else if (n < 0)
      n = (n % mod + mod) % mod;
  }
  operator int() { return n; }
};
bool operator==(modint a, modint b) { return a.n == b.n; }
modint operator+=(modint &a, modint b) {
  a.n += b.n;
  if (a.n >= mod) a.n -= mod;
  return a;
}
modint operator-=(modint &a, modint b) {
  a.n -= b.n;
  if (a.n < 0) a.n += mod;
  return a;
}
modint operator*=(modint &a, modint b) {
  a.n = ((long long)a.n * b.n) % mod;
  return a;
}
modint operator+(modint a, modint b) { return a += b; }
modint operator-(modint a, modint b) { return a -= b; }
modint operator*(modint a, modint b) { return a *= b; }
modint operator^(modint a, int n) {
  if (n == 0) return modint(1);
  modint res = (a * a) ^ (n / 2);
  if (n % 2) res = res * a;
  return res;
}
long long inv(long long a, long long p) {
  return (a == 1 ? 1 : (1 - p * inv(p % a, a)) / a + p);
}
modint operator/(modint a, modint b) { return a * modint(inv(b, mod)); }
const int max_n = 1 << 18;
modint fact[max_n], factinv[max_n];
void init_f() {
  fact[0] = modint(1);
  for (int i = 0; i < max_n - 1; i++) {
    fact[i + 1] = fact[i] * modint(i + 1);
  }
  factinv[max_n - 1] = modint(1) / fact[max_n - 1];
  for (int i = max_n - 2; i >= 0; i--) {
    factinv[i] = factinv[i + 1] * modint(i + 1);
  }
}
modint comb(int a, int b) {
  if (a < 0 || b < 0 || a < b) return 0;
  return fact[a] * factinv[b] * factinv[a - b];
}
using mP = pair<modint, modint>;
int dx[4] = {0, 1, 0, -1};
int dy[4] = {1, 0, -1, 0};
struct SuffixArray {
  struct SAComp {
    const int h;
    const vector<int> &g;
    SAComp(int h, vector<int> &g) : h(h), g(g) { ; }
    bool operator()(int a, int b) {
      return a != b && (g[a] != g[b] ? g[a] < g[b] : g[a + h] < g[b + h]);
    }
  };
  int n;
  string str;
  vector<int> sa, lcp;
  SuffixArray(const string &t) : n(t.size()), sa(n + 1), lcp(n + 1) {
    str = t;
    vector<int> g(n + 1, 0), b(n + 1, 0);
    for (int i = 0; i < n + 1; i++) {
      sa[i] = i;
      g[i] = str[i];
    }
    sort(begin(sa), end(sa), SAComp(0, g));
    for (int h = 1; b[n] != n; h *= 2) {
      SAComp comp(h, g);
      sort(sa.begin(), sa.end(), comp);
      for (int i = 0; i < n; i++) b[i + 1] = b[i] + comp(sa[i], sa[i + 1]);
      for (int i = 0; i < n + 1; i++) g[sa[i]] = b[i];
    }
    int h = 0;
    for (int i = 0; i < n + 1; i++) b[sa[i]] = i;
    for (int i = 0; i < n + 1; i++) {
      if (b[i]) {
        for (int j = sa[b[i] - 1];
             j + h < n && i + h < n && str[j + h] == str[i + h]; ++h)
          ;
        lcp[b[i]] = h;
      } else {
        lcp[b[i]] = -1;
      }
      if (h > 0) --h;
    }
  }
  ~SuffixArray() { str.clear(); }
};
void solve() {
  int N, M;
  cin >> N >> M;
  vector<int> s(M), c(M);
  for (int i = 0; i < M; i++) {
    cin >> s[i] >> c[i];
    s[i]--;
  }
  bool b = false;
  int ans = -1;
  for (int i = 0; i < 1000; i++) {
    string str = to_string(i);
    if (str.size() != N) continue;
    bool temp = true;
    for (int j = 0; j < M; j++) {
      if (str[s[j]] != to_string(c[j])[0]) {
        temp = false;
        break;
      }
    }
    if (temp) {
      ans = i;
      b = true;
      break;
    }
  }
  if (M == 0) ans = 0;
  cout << ans << endl;
}
signed main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  solve();
  char nyaa;
  cin >> nyaa;
  return 0;
}
