#include <bits/stdc++.h>
template <typename T>
void MACRO_VAR_Scan(T& t) {
  std::cin >> t;
}
template <typename First, typename... Rest>
void MACRO_VAR_Scan(First& first, Rest&... rest) {
  std::cin >> first;
  MACRO_VAR_Scan(rest...);
}
template <typename T>
void MACRO_VEC_ROW_Init(int n, T& t) {
  t.resize(n);
}
template <typename First, typename... Rest>
void MACRO_VEC_ROW_Init(int n, First& first, Rest&... rest) {
  first.resize(n);
  MACRO_VEC_ROW_Init(n, rest...);
}
template <typename T>
void MACRO_VEC_ROW_Scan(int p, T& t) {
  std::cin >> t[p];
}
template <typename First, typename... Rest>
void MACRO_VEC_ROW_Scan(int p, First& first, Rest&... rest) {
  std::cin >> first[p];
  MACRO_VEC_ROW_Scan(p, rest...);
}
template <typename T>
void MACRO_OUT(const T t) {
  std::cout << t;
}
template <typename First, typename... Rest>
void MACRO_OUT(const First first, const Rest... rest) {
  std::cout << first << " ";
  MACRO_OUT(rest...);
}
template <class T>
inline T CHMAX(T& a, const T b) {
  return a = (a < b) ? b : a;
}
template <class T>
inline T CHMIN(T& a, const T b) {
  return a = (a > b) ? b : a;
}
template <class T>
using V = std::vector<T>;
template <class T>
using VV = V<V<T>>;
template <typename S, typename T>
std::ostream& operator<<(std::ostream& os, std::pair<S, T> p) {
  os << "(" << p.first << ", " << p.second << ")";
  return os;
}
using ll = long long;
using ull = unsigned long long;
using ld = long double;
using PAIR = std::pair<ll, ll>;
using PAIRLL = std::pair<ll, ll>;
constexpr ll INFINT = (1 << 30) - 1;
constexpr ll INFINT_LIM = (1LL << 31) - 1;
constexpr ll INFLL = 1LL << 60;
constexpr ll INFLL_LIM = (1LL << 62) - 1 + (1LL << 62);
constexpr double eps = 1e-7;
constexpr ll MOD = 1000000007;
constexpr double PI = 3.141592653589793238462643383279;
template <class T, size_t N>
void FILL(T (&a)[N], const T& val) {
  for (auto& x : a) x = val;
}
template <class ARY, size_t N, size_t M, class T>
void FILL(ARY (&a)[N][M], const T& val) {
  for (auto& b : a) FILL(b, val);
}
template <class T>
void FILL(std::vector<T>& a, const T& val) {
  for (auto& x : a) x = val;
}
template <class ARY, class T>
void FILL(std::vector<std::vector<ARY>>& a, const T& val) {
  for (auto& b : a) FILL(b, val);
}
signed main() {
  std::ios::sync_with_stdio(false);
  std::cin.tie(0);
  ;
  ll n, m;
  MACRO_VAR_Scan(n, m);
  ;
  std::vector<ll> s, c;
  MACRO_VEC_ROW_Init(m, s, c);
  for (ll w_ = 0; w_ < m; ++w_) {
    MACRO_VEC_ROW_Scan(w_, s, c);
  };
  V<ll> d(n, -1);
  for (ll i = 0; i < ll(m); ++i) {
    --s[i];
    if (d[s[i]] != -1) {
      if (d[s[i]] == c[i]) continue;
      MACRO_OUT(-1);
      std::cout << "\n";
      ;
      return 0;
    } else {
      d[s[i]] = c[i];
    }
  }
  for (ll i = 0; i < ll(n); ++i) {
    if (d[i] == -1) {
      if (i == 0)
        d[i] = 1;
      else
        d[i] = 0;
    }
  }
  if (d[0] == 0) {
    MACRO_OUT(-1);
    std::cout << "\n";
    ;
    return 0;
  }
  for (ll i = 0; i < ll(n); ++i) {
    MACRO_OUT(d[i]);
    ;
  }
  std::cout << "\n";
  ;
  return 0;
}
