#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using Edge = int;
using Graph = vector<vector<Edge>>;
const ll MOD = 1000000007;
const ll nmax = 8;
const ll INF = 1e9;
const int MAX = 510000;
bool graph[nmax][nmax];
long long fac[MAX], finv[MAX], inv[MAX];
void COMinit() {
  fac[0] = fac[1] = 1;
  finv[0] = finv[1] = 1;
  inv[1] = 1;
  for (int i = 2; i < MAX; i++) {
    fac[i] = fac[i - 1] * i % MOD;
    inv[i] = MOD - inv[MOD % i] * (MOD / i) % MOD;
    finv[i] = finv[i - 1] * inv[i] % MOD;
  }
}
ll COM(int n, int k) {
  if (n < k) return 0;
  if (n < 0 || k < 0) return 0;
  return fac[n] * (finv[k] * finv[n - k] % MOD) % MOD;
}
vector<vector<ll>> dist = vector<vector<ll>>(nmax, vector<ll>(nmax, INF));
struct SegmentTree {
 private:
  ll n;
  vector<ll> node;

 public:
  SegmentTree(vector<ll> v) {
    ll sz = v.size();
    n = 1;
    while (n < sz) {
      n *= 2;
    }
    node.resize(2 * n - 1, INF);
    for (ll i = 0; i < sz; i++) {
      node[i + n - 1] = v[i];
    }
    for (ll i = n - 2; i >= 0; i--) {
      node[i] = min(node[2 * i + 1], node[2 * i + 2]);
    }
  }
  void update(ll x, ll val) {
    x += (n - 1);
    node[x] = val;
    while (x > 0) {
      x = (x - 1) / 2;
      node[x] = min(node[2 * x + 1], node[2 * x + 2]);
    }
  }
  ll find(ll a, ll b, ll k = 0, ll l = 0, ll r = -1) {
    if (r < 0) r = n;
    if (r <= a || b <= l) return INF;
    if (a <= l && r <= b) return node[k];
    ll vl = find(a, b, 2 * k + 1, l, (l + r) / 2);
    ll vr = find(a, b, 2 * k + 2, (l + r) / 2, r);
    return min(vl, vr);
  }
};
void warshall_floyd(ll n) {
  for (size_t i = 0; i < n; i++) {
    for (size_t j = 0; j < n; j++) {
      for (size_t k = 0; k < n; k++) {
        dist[j][k] = min(dist[j][k], dist[j][i] + dist[i][k]);
      }
    }
  }
}
class UnionFind {
 public:
  vector<ll> Parent;
  UnionFind(ll N) { Parent = vector<ll>(N, -1); }
  ll find(ll A) {
    if (Parent[A] < 0) return A;
    return Parent[A] = find(Parent[A]);
  }
  ll size(ll A) { return -Parent[find(A)]; }
  bool Union(ll A, ll B) {
    A = find(A);
    B = find(B);
    if (A == B) {
      return false;
    }
    if (size(A) < size(B)) swap(A, B);
    Parent[A] += Parent[B];
    Parent[B] = A;
    return true;
  }
};
ll gcd(ll a, ll b) {
  if (b == 0) return a;
  return gcd(b, a % b);
}
ll lcm(ll a, ll b) {
  ll g = gcd(a, b);
  return a / g * b;
}
ll mulMod(ll a, ll b) { return (((a % MOD) * (b % MOD)) % MOD); }
ll powMod(ll a, ll p) {
  if (p == 0) {
    return 1;
  } else if (p % 2 == 0) {
    ll half = powMod(a, p / 2);
    return mulMod(half, half);
  } else {
    return mulMod(powMod(a, p - 1), a);
  }
}
ll ceil(ll a, ll b) { return (a + b - 1) / b; }
vector<ll> tsort(Graph G) {
  ll N = G.size();
  vector<ll> in(N);
  for (auto &&edges : G) {
    for (auto &&edge : edges) {
      in[edge]++;
    }
  }
  queue<int> que;
  for (int i = 0; i < N; i++) {
    if (in[i] == 0) {
      que.push(i);
    }
  }
  int cnt = 0;
  vector<ll> ans;
  while (!que.empty()) {
    int v = que.front();
    que.pop();
    ans.push_back(v);
    for (auto &&next : G[v]) {
      in[next]--;
      if (in[next] == 0) {
        que.push(next);
      }
    }
  }
  return ans;
}
Graph G(100);
void treeDFS(int from, int current, int dist, int &maxDist, int &maxVertex) {
  if (dist > maxDist) {
    maxDist = dist;
    maxVertex = current;
  }
  for (auto to : G[current]) {
    if (to == from) continue;
    treeDFS(current, to, dist + 1, maxDist, maxVertex);
  }
}
pair<int, int> getTreeDiameter() {
  int start = 0, end = 0, maxDist = 0;
  treeDFS(-1, start, 0, maxDist, end);
  start = end, end = 0, maxDist = 0;
  treeDFS(-1, start, 0, maxDist, end);
  return make_pair(start, end);
}
void solve(long long N, long long M, std::vector<long long> s,
           std::vector<long long> c) {
  vector<ll> ans(N, -1);
  for (int i = 0; i < M; i++) {
    if (ans[s[i] - 1] != -1 && ans[s[i] - 1] != c[i]) {
      cout << -1 << endl;
      return;
    }
    ans[s[i] - 1] = c[i];
  }
  bool flag = false;
  if (ans[0] == 0 && N != 1) {
    cout << -1 << endl;
    return;
  }
  for (int i = 0; i < N; i++) {
    if (ans[i] == -1) {
      cout << 0;
    } else {
      cout << ans[i];
    }
  }
  cout << endl;
}
int main() {
  long long N;
  scanf("%lld", &N);
  long long M;
  scanf("%lld", &M);
  std::vector<long long> s(M);
  std::vector<long long> c(M);
  for (int i = 0; i < M; i++) {
    scanf("%lld", &s[i]);
    scanf("%lld", &c[i]);
  }
  solve(N, M, std::move(s), std::move(c));
  return 0;
}
