#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using pii = pair<int, int>;
using pll = pair<ll, ll>;
using vi = vector<int>;
using vl = vector<ll>;
using decendingQueue = priority_queue<ll, vl>;
using ascendingQueue = priority_queue<ll, vl, greater<ll>>;
const int dx[4] = {1, 0, -1, 0}, dy[4] = {0, 1, 0, -1};
const int INT_INF = 1e9;
const ll LL_INF = 1e18;
const int mod = 1000000007;
template <class T>
void mySort(vector<T> &X, bool isAscending) {
  if (isAscending) {
    sort((X).begin(), (X).end());
  } else {
    sort((X).begin(), (X).end(), greater<T>());
  }
}
long long gcd(long long m, long long n) {
  if (m < n) return gcd(n, m);
  if (n == 0) return m;
  return gcd(n, m % n);
}
long long lcm(long long m, long long n) { return m * (n / gcd(m, n)); }
struct mint {
  ll x;
  mint(ll x = 0) : x((x % mod + mod) % mod) {}
  mint &operator+=(const mint a) {
    if ((x += a.x) >= mod) x -= mod;
    return *this;
  }
  mint &operator-=(const mint a) {
    if ((x += mod - a.x) >= mod) x -= mod;
    return *this;
  }
  mint &operator*=(const mint a) {
    (x *= a.x) %= mod;
    return *this;
  }
  mint operator+(const mint a) const {
    mint res(*this);
    return res += a;
  }
  mint operator-(const mint a) const {
    mint res(*this);
    return res -= a;
  }
  mint operator*(const mint a) const {
    mint res(*this);
    return res *= a;
  }
  mint pow(ll t) const {
    if (!t) return 1;
    mint a = pow(t >> 1);
    a *= a;
    if (t & 1) a *= *this;
    return a;
  }
  mint inv() const { return pow(mod - 2); }
  mint &operator/=(const mint a) { return (*this) *= a.inv(); }
  mint operator/(const mint a) const {
    mint res(*this);
    return res /= a;
  }
};
struct combination {
  vector<mint> fact, ifact;
  combination(int n) : fact(n + 1), ifact(n + 1) {
    assert(n < mod);
    fact[0] = 1;
    for (int i = 1; i <= n; ++i) fact[i] = fact[i - 1] * i;
    ifact[n] = fact[n].inv();
    for (int i = n; i >= 1; --i) ifact[i - 1] = ifact[i] * i;
  }
  mint operator()(int n, int k) {
    if (k < 0 || k > n) return 0;
    return fact[n] * ifact[k] * ifact[n - k];
  }
};
vector<long long> SieveOfEratosthenes(int max) {
  vector<long long> sieve;
  vector<long long> primes;
  for (int i = 1; i < max + 1; ++i) {
    sieve.push_back(i);
  }
  sieve[0] = 0;
  for (int i = 2; i < max + 1; ++i) {
    if (sieve[i - 1] != 0) {
      primes.push_back(sieve[i - 1]);
      for (int j = 2 * sieve[i - 1]; j < max + 1; j += sieve[i - 1]) {
        sieve[j - 1] = 0;
      }
    }
  }
  return primes;
}
class UnionFindTree {
 private:
  vector<int> par;
  vector<int> rnk;
  vector<int> siz;

 public:
  UnionFindTree(int n) {
    par.assign(n, -1);
    rnk.assign(n, -1);
    siz.assign(n, -1);
    for (int i = 0; i < n; ++i) {
      par[i] = i;
      rnk[i] = 0;
      siz[i] = 1;
    }
  }
  int find(int x) {
    if (par[x] == x)
      return x;
    else
      return par[x] = find(par[x]);
  }
  bool same(int x, int y) { return find(x) == find(y); }
  void unite(int x, int y) {
    x = find(x);
    y = find(y);
    if (x == y) return;
    if (rnk[x] < rnk[y]) {
      par[x] = y;
      siz[y] += siz[x];
    } else {
      par[y] = x;
      siz[x] += siz[y];
      if (rnk[x] == rnk[y]) ++rnk[x];
    }
  }
  int size(int x) {
    x = find(x);
    return siz[x];
  }
};
class Edge {
 public:
  ll from;
  ll to;
  ll cost;
  Edge() {}
  Edge(ll from, ll to, ll cost) {
    this->from = from;
    this->to = to;
    this->cost = cost;
  }
  bool operator<(const Edge &edge) const { return cost < edge.cost; }
};
class Graph {
 public:
  ll nodes;
  vector<Edge> edges;
  Graph() {}
  Graph(ll nodes) { this->nodes = nodes; }
  void addEdge(ll from, ll to, ll cost) {
    this->edges.push_back(Edge(from, to, cost));
  }
};
class Kruskal {
 private:
  Graph graph;
  vector<Edge> MinimumSpanningTree;
  ll minimumCost;
  void searchMinimumSpanningTree() {
    UnionFindTree uf(graph.nodes);
    sort((graph.edges).begin(), (graph.edges).end());
    for (auto edge : graph.edges) {
      if (!uf.same(edge.from, edge.to)) {
        uf.unite(edge.from, edge.to);
        MinimumSpanningTree.push_back(edge);
      }
    }
  }

 public:
  Kruskal(Graph graph) { this->graph = graph; }
  ll getMinimumSpanningTreeCost() {
    searchMinimumSpanningTree();
    ll cost = 0;
    for (auto tr : MinimumSpanningTree) {
      cost += tr.cost;
    }
    return cost;
  }
};
class Dijkstra {
 private:
  Graph graph;
  map<ll, vector<Edge>> fromPaths;
  vl distances;
  vl srcs;

 public:
  Dijkstra(Graph graph) {
    this->graph = graph;
    for (auto edge : graph.edges) {
      fromPaths[edge.from].push_back(edge);
    }
  }
  void searchMinimumPathFrom(ll src) {
    distances = vl(graph.nodes + 1, LL_INF);
    srcs = vl(graph.nodes + 1, LL_INF);
    priority_queue<pll, vector<pll>, greater<pll>> pq;
    distances[src] = 0;
    srcs[src] = -1;
    pq.push(make_pair(0ll, src));
    while (!pq.empty()) {
      int u = pq.top().second;
      double uw = pq.top().first;
      pq.pop();
      if (distances[u] < uw) {
        continue;
      };
      for (auto edge : fromPaths[u]) {
        int v = edge.to;
        ll w = edge.cost;
        if (distances[v] > distances[u] + w) {
          distances[v] = distances[u] + w;
          srcs[v] = u;
          pq.push(make_pair(distances[v], v));
        }
      }
    }
  };
  ll getDistance(ll n) { return distances[n]; }
  ll getFrom(ll n) { return srcs[n]; }
};
class BellmanFord {
 private:
  Graph graph;
  vector<bool> hasNegativeCycles;
  vector<ll> distances;
  vl srcs;

 public:
  BellmanFord(Graph graph) {
    ll nodes = graph.nodes + 1;
    this->graph = graph;
    distances = vector<ll>(nodes, LL_INF);
    hasNegativeCycles = vector<bool>(nodes, false);
  }
  void searchMinimumPathFrom(ll src) {
    distances[src] = 0;
    for (ll i = 0; i < graph.nodes - 1; i++) {
      for (auto edge : graph.edges) {
        ll u = edge.from;
        ll v = edge.to;
        ll w = edge.cost;
        if (distances[u] != LL_INF) {
          distances[v] = min(distances[v], distances[u] + w);
        }
      }
    }
    for (auto edge : graph.edges) {
      ll u = edge.from;
      ll v = edge.to;
      ll w = edge.cost;
      if (distances[u] == LL_INF) {
        continue;
      }
      if (distances[u] + w < distances[v]) {
        hasNegativeCycles[v] = true;
      }
    }
    for (ll i = 0; i < graph.nodes; i++) {
      for (auto edge : graph.edges) {
        ll u = edge.from;
        ll v = edge.to;
        ll w = edge.cost;
        if (distances[u] == LL_INF) {
          continue;
        }
        distances[v] = min(distances[v], distances[u] + w);
        if (hasNegativeCycles[u] == true) {
          hasNegativeCycles[v] = true;
        }
      }
    }
  }
  ll getDistance(ll n) { return distances[n]; }
  bool hasNegativeCycle(ll n) { return hasNegativeCycles[n]; }
  ll getFrom(ll n) { return srcs[n]; }
};
class WarshallFloyd {
 private:
  Graph graph;
  int nodes = this->graph.nodes + 1;
  vector<vector<ll>> distances;

 public:
  WarshallFloyd(Graph graph) {
    this->graph = graph;
    nodes = this->graph.nodes + 1;
    this->distances = vector<vector<ll>>(nodes, vector<ll>(nodes, LL_INF));
    for (auto edge : graph.edges) {
      int from = edge.from;
      int to = edge.to;
      int cost = edge.cost;
      distances[from][to] = cost;
    }
  }
  void searchMinimumPath() {
    for (int k = 0; k < nodes; k++) {
      for (int i = 0; i < nodes; i++) {
        for (int j = 0; j < nodes; j++) {
          if (distances[i][k] == LL_INF || distances[k][j] == LL_INF) {
            continue;
          }
          if (distances[i][k] + distances[k][j] < distances[i][j]) {
            distances[i][j] = distances[i][k] + distances[k][j];
          }
        }
      }
    }
  }
  ll getDistance(int from, int to) { return distances[from][to]; }
};
void solve(long long N, long long M, std::vector<long long> s,
           std::vector<long long> c) {
  for (int(i) = (0); (i) < (M); ++(i)) {
    s[i]--;
  }
  vector<int> str(N, -1);
  for (int(i) = (0); (i) < (M); ++(i)) {
    if (str[s[i]] == -1) {
      str[s[i]] = c[i];
    } else if (str[s[i]] != c[i]) {
      cout << -1 << endl;
      return;
    }
  }
  if (N != 1 && str[0] <= 0) {
    cout << -1 << endl;
    return;
  }
  for (int(i) = (0); (i) < (N); ++(i)) {
    if (str[i] == -1) {
      cout << "0";
    } else {
      cout << str[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;
}
