#include <bits/stdc++.h>
using namespace std;
template <typename T>
ostream &operator<<(ostream &os, const vector<T> &A) {
  for (long long i = 0; i < A.size(); i++) os << A[i] << " ";
  os << endl;
  return os;
}
template <>
ostream &operator<<(ostream &os, const vector<vector<long long> > &A) {
  long long N = A.size();
  long long M;
  if (N > 0) M = A[0].size();
  for (long long i = 0; i < N; i++) {
    for (long long j = 0; j < M; j++) os << A[i][j] << " ";
    os << endl;
  }
  return os;
}
struct edge {
  long long from, to, d, c;
  edge(long long _from = 0, long long _to = 0, long long _d = 0,
       long long _c = 0) {
    from = _from;
    to = _to;
    d = _d;
    c = _c;
  }
  bool operator<(const edge &rhs) const {
    return (d == rhs.d) ? (c < rhs.c) : (d < rhs.d);
  }
};
struct aabb {
  long long x1, y1, x2, y2;
  aabb(long long x1, long long y1, long long x2, long long y2)
      : x1(x1), y1(y1), x2(x2), y2(y2) {}
};
struct flow {
  long long to, cap, rev, cost;
  flow(long long to = 0, long long cap = 0, long long rev = 0,
       long long cost = 0)
      : to(to), cap(cap), rev(rev), cost(cost) {}
};
const long long di[4] = {0, -1, 0, 1};
const long long dj[4] = {-1, 0, 1, 0};
const long long ci[5] = {0, 0, -1, 0, 1};
const long long cj[5] = {0, -1, 0, 1, 0};
const long long LINF = LLONG_MAX / 2;
const long long INF = INT_MAX / 2;
const double PI = acos(-1);
long long pow2(long long n) { return 1LL << n; }
template <typename T, typename U>
bool chmin(T &x, const U &y) {
  if (x > y) {
    x = y;
    return true;
  }
  return false;
}
template <typename T, typename U>
bool chmax(T &x, const U &y) {
  if (x < y) {
    x = y;
    return true;
  }
  return false;
}
struct initializer {
  initializer() { cout << fixed << setprecision(20); }
};
initializer _____;
long long N, M, K, T, Q, H, W;
signed main() {
  cin >> N >> M;
  vector<pair<long long, long long> > A(M);
  for (long long i = 0; i < (long long)(M); i++) {
    cin >> A[i].first >> A[i].second;
  }
  K = 1;
  for (long long i = 0; i < (long long)(N); i++) K *= 10;
  for (long long j = 0; j < (long long)(K); j++) {
    if (!j) continue;
    if (j < K / 10) continue;
    bool f = false;
    for (long long i = 0; i < (long long)(M); i++) {
      long long ten = 1;
      for (long long l = 0; l < (long long)(N - A[i].first); l++) ten *= 10;
      if (j / ten % 10 != A[i].second) {
        f = true;
        break;
      }
    }
    if (f) continue;
    cout << j << endl;
    return 0;
  }
  cout << -1 << endl;
  return 0;
}
