#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ld = long double;
using pll = pair<ll, ll>;
using graph = vector<vector<int>>;
const ll MOD = 1e9 + 7;
const ld EPS = 1e-9;
const int dx[4] = {1, 0, -1, 0};
const int dy[4] = {0, 1, 0, -1};
const int edx[8] = {1, 1, 0, -1, -1, -1, 0, 1};
const int edy[8] = {0, 1, 1, 1, 0, -1, -1, -1};
template <class T>
void chmin(T &a, T b) {
  a = min(a, b);
}
template <class T>
void chmax(T &a, T b) {
  a = max(a, b);
}
ll modpow(ll a, ll b, ll p = MOD) {
  ll ret = 1;
  while (b != 0) {
    if ((b & 1) == 1) ret *= a;
    a *= a;
    if (a >= p) a %= p;
    if (ret >= p) ret %= p;
    b >>= 1;
  }
  return ret;
}
int digit(ll x, ll base = 10) {
  int ret = 0;
  while (x) {
    x /= base;
    ret++;
  }
  return ret;
}
int sumOfDigit(ll x) {
  int ret = 0;
  while (x) {
    ret += x % 10;
    x /= 10;
  }
  return ret;
}
ll factrial(int n) {
  ll ret = 1;
  for (int i = 1; i <= n; i++) {
    ret *= i;
  }
  return ret;
}
ll gcd(ll a, ll b) {
  while (b != 0) {
    a %= b;
    swap(a, b);
  }
  return a;
}
ll lcm(ll a, ll b) { return a / gcd(a, b) * b; }
ll modinv(ll a, ll p = MOD) {
  ll b = p, u = 1, v = 0;
  while (b) {
    ll tmp = a / b;
    a -= tmp * b;
    u -= tmp * v;
    swap(a, b);
    swap(u, v);
  }
  u %= p;
  if (u < 0) u += p;
  return u;
}
bool isprime(ll p) {
  if (p <= 1) return false;
  ll s = min(p - 1, (ll)ceil(sqrt(p)));
  for (int i = 2; i <= s; i++)
    if (p % i == 0) return false;
  return true;
}
ll minDivisor(ll x, ll n = 2) {
  if (x <= 1) return 1;
  ll s = min(x - 1, (ll)ceil(sqrt(x)));
  for (int i = n; i <= s; i++)
    if (x % i == 0) return i;
  return x;
}
ll countDivisor(ll x) {
  map<ll, int> m;
  if (x <= 1) return 1;
  ll s = min(x - 1, (ll)ceil(sqrt(x)));
  for (int i = 2; i <= s; i++) {
    if (x % i == 0) {
      x /= i;
      m[i]++;
      i = 1;
    }
  }
  if (x != 1) m[x]++;
  ll ret = 1;
  for (auto i : m) {
    ret *= i.second + 1;
  }
  return ret;
}
class disjoint_set {
  vector<int> _parent, _size;

 public:
  disjoint_set(int n) : _parent(n), _size(n) {
    for (int i = 0; i < n; i++) {
      _parent[i] = i;
      _size[i] = 1;
    }
  }
  int root(int x) {
    if (_parent[x] == x) return x;
    return _parent[x] = root(_parent[x]);
  }
  void unite(int x, int y) {
    int rx = root(x);
    int ry = root(y);
    if (rx == ry) return;
    _parent[rx] = ry;
    _size[ry] += _size[rx];
  }
  bool same(int x, int y) { return root(x) == root(y); }
  int size(int x) { return _size[root(x)]; }
};
void init() {
  cin.tie(nullptr);
  ios_base::sync_with_stdio(false);
  cout << fixed << setprecision(15);
}
void solve() {
  int n, m;
  cin >> n >> m;
  int a[n];
  for (int i = 0; i < n; i++) {
    a[i] = -1;
  }
  bool flg = false;
  for (int i = 0; i < m; i++) {
    int s, c;
    cin >> s >> c;
    s--;
    if (s >= n) {
      flg = true;
    }
    if (a[s] == -1)
      a[s] = c;
    else if (a[s] != c) {
      flg = true;
    }
  }
  if (flg || a[0] == 0) {
    cout << -1 << endl;
    return;
  }
  for (int i = 0; i < n; i++) {
    if (a[i] == -1) {
      cout << 1;
    } else {
      cout << a[i];
    }
  }
  cout << endl;
}
int main() {
  init();
  solve();
  return 0;
}
