#include <bits/stdc++.h>
const int LG = 21;
const int FN = 400005;
const long long MOD = 998244353;
const long long INF = 1e9;
const long long INFLL = 1e18;
const double PI = acos(-1);
using namespace std;
int cx[4] = {-1, 0, 1, 0};
int cy[4] = {0, -1, 0, 1};
string Yes[2] = {"No", "Yes"};
string YES[2] = {"NO", "YES"};
string Psb[2] = {"Impossible", "Possible"};
string psb[2] = {"impossible", "possible"};
long long inq(long long x, long long y) {
  if (!y) return 1 % MOD;
  long long l = inq(x, y / 2);
  if (y % 2) return l * l % MOD * x % MOD;
  return l * l % MOD;
}
long long rev(long long x) { return inq(x, MOD - 2); }
bool __precomputed_combinatorics = 0;
vector<long long> __fact, __ufact, __rev;
void __precompute_combinatorics() {
  __precomputed_combinatorics = 1;
  __fact.resize(FN);
  __ufact.resize(FN);
  __rev.resize(FN);
  __rev[1] = 1;
  for (int i = 2; i < FN; i++)
    __rev[i] = MOD - __rev[MOD % i] * (MOD / i) % MOD;
  __fact[0] = 1, __ufact[0] = 1;
  for (int i = 1; i < FN; i++)
    __fact[i] = __fact[i - 1] * i % MOD,
    __ufact[i] = __ufact[i - 1] * __rev[i] % MOD;
}
long long fact(int x) {
  if (!__precomputed_combinatorics) __precompute_combinatorics();
  return __fact[x];
}
long long cnk(int n, int k) {
  if (k < 0 || k > n) return 0;
  if (!__precomputed_combinatorics) __precompute_combinatorics();
  return __fact[n] * __ufact[n - k] % MOD * __ufact[k] % MOD;
}
int Root(int x, vector<int> &root) {
  if (x == root[x]) return x;
  return root[x] = Root(root[x], root);
}
void Merge(int v, int u, vector<int> &root, vector<int> &sz) {
  v = Root(v, root), u = Root(u, root);
  if (v == u) return;
  if (sz[v] < sz[u]) {
    sz[u] += sz[v];
    root[v] = u;
  } else {
    sz[v] += sz[u];
    root[u] = v;
  }
}
int ok(int x, int n) { return 0 <= x && x < n; }
void bfs(int v, vector<int> &dist, vector<vector<int> > &graph) {
  fill((dist).begin(), (dist).end(), -1);
  dist[v] = 0;
  vector<int> q = {v};
  for (int i = 0; i < q.size(); i++) {
    for (auto u : graph[q[i]]) {
      if (dist[u] == -1) {
        dist[u] = dist[q[i]] + 1;
        q.push_back(u);
      }
    }
  }
}
double sqr(double x) { return x * x; }
double dist(double x1, double y1, double x2, double y2) {
  return sqrt(sqr(x1 - x2) + sqr(y1 - y2));
}
signed main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  long long n, m;
  cin >> n >> m;
  vector<int> g(n, -1);
  for (int(i) = 0; (i) != (m); (i)++) {
    int s, c;
    cin >> s >> c;
    s--;
    if (g[s] == -1) g[s] = c;
    if (g[s] != c) cout << -1, exit(0);
  }
  if (g[0] == 0 && n != 1) cout << -1, exit(0);
  for (int(i) = 0; (i) != (n); (i)++) cout << abs(g[i]);
}
