#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ld = long double;
using vi = vector<int>;
using vvi = vector<vi>;
using vll = vector<ll>;
using vvll = vector<vll>;
using vb = vector<bool>;
using vs = vector<string>;
template <class T>
inline void chmax(T& a, T b) {
  a = std::max(a, b);
}
template <class T>
inline void chmin(T& a, T b) {
  a = std::min(a, b);
}
template <ll ModVal>
struct ModInt {
  ll x;
  ModInt(ll _x = 0) : x((_x % ModVal + ModVal) % ModVal) {}
  ModInt operator-() const { return ModInt(-x); }
  ModInt& operator+=(const ModInt a) {
    x += a.x;
    if (x >= ModVal) x -= ModVal;
    return *this;
  }
  ModInt& operator-=(const ModInt a) {
    x = x + ModVal - a.x;
    if (x >= ModVal) x -= ModVal;
    return *this;
  }
  ModInt& operator*=(const ModInt a) {
    x *= a.x;
    x %= ModVal;
    return *this;
  }
  ll ext_gcd(ll a, ll b, ll& x, ll& y) {
    if (b == 0) {
      x = 1;
      y = 0;
      return a;
    }
    ll tmp = a / b;
    ll d = ext_gcd(b, a - b * tmp, y, x);
    y -= tmp * x;
    return d;
  }
  ModInt inv(const ModInt a) {
    ll u, v;
    ext_gcd(a.x, ModVal, u, v);
    return ModInt(u);
  }
  ModInt& operator/=(const ModInt a) { return (*this) *= inv(a); }
  ModInt operator+(const ModInt a) const {
    ModInt retval(*this);
    return retval += a;
  }
  ModInt operator-(const ModInt a) const {
    ModInt retval(*this);
    return retval -= a;
  }
  ModInt operator*(const ModInt a) const {
    ModInt retval(*this);
    return retval *= a;
  }
  ModInt operator/(const ModInt a) const {
    ModInt retval(*this);
    return retval /= a;
  }
  ModInt pow(ll n) {
    ModInt ans(1);
    while (n) {
      if (n & 1) ans = ans * x;
      *this = (*this) * (*this);
      n = n >> 1;
    }
    return ans;
  }
  constexpr const ll& value() { return this->x; }
};
template <ll ModVal>
ostream& operator<<(ostream& os, const ModInt<ModVal>& a) {
  os << a.x;
  return os;
}
using mint = ModInt<(ll)(1e9 + 7)>;
template <typename T>
class Combination {
 public:
  Combination(ll _max_n) : max_n(_max_n), factional(max_n + 1), inv(max_n + 1) {
    factional[0] = 1;
    inv[0] = 1;
    for (ll i = 0; i < max_n; i++) {
      factional[i + 1] = factional[i] * (i + 1);
      inv[i + 1] = inv[i] / (i + 1);
    }
  }
  T choose(ll n, ll k) {
    if (n == 0 && k == 0) return 1;
    if (n < k || n < 0) return 0;
    T tmp = inv[n - k] * inv[k];
    return tmp * factional[n];
  }

 private:
  const ll max_n;
  std::vector<T> factional;
  std::vector<T> inv;
};
using Comb = Combination<mint>;
signed main() {
  cin.tie(0);
  ios::sync_with_stdio(false);
  cout << fixed << setprecision(20);
  ll n, m;
  cin >> n >> m;
  vll s(m);
  vll c(m);
  for (ll i = 0; i < m; i++) {
    cin >> s[i] >> c[i];
  }
  vll t(5);
  t[1] = 1;
  t[2] = 10;
  t[3] = 100;
  t[4] = 1000;
  for (ll a = t[n]; a < t[n + 1]; a++) {
    bool match = true;
    for (ll i = 0; i < m; i++) {
      if ((a / t[n - s[i] + 1]) % 10 != c[i]) {
        match = false;
        break;
      }
    }
    if (match) {
      cout << a << endl;
      return 0;
    }
  }
  cout << -1 << endl;
  return 0;
}
