#include <bits/stdc++.h>
template <typename T>
class mylist {
 private:
  std::vector<char> alphabets = {'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i',
                                 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r',
                                 's', 't', 'u', 'v', 'w', 'x', 'y', 'z'};

 public:
  mylist(long long i) { list.resize(i); }
  mylist() {}
  void input();
  std::vector<T> list;
  void sort();
  std::vector<T> sorted();
  std::vector<size_t> argsort();
  int find(T key);
  T pop(size_t i);
  void push(T value);
  void push(mylist<T> list_);
  mylist<T> iloc(mylist<T> list_);
  std::string toString();
  void fromString(std::string string);
  void fromAlphabets(std::string string);
  std::string toAlphabets(bool upper);
  template <typename V>
  void add(V value);
  void range();
  void range(long long length);
  void range(long long start, long long end);
  size_t min_index();
  T min();
  size_t max_index();
  T max();
};
namespace mystd {
long long MOD = std::pow(10, 9) + 7;
size_t fac_size = std::pow(10, 5);
bool calcurated_fac = false;
std::vector<long long> fac;
std::vector<long long> ifac;
template <typename T>
T factorical(T a);
template <typename T>
T LCM(T a, T b);
template <typename T>
T GCD(T a, T b);
template <typename T>
T LCM(std::vector<T> A);
template <typename T>
T GCD(std::vector<T> A);
template <typename T>
T LCM(mylist<T> A);
template <typename T>
T GCD(mylist<T> A);
long long pow(long long x, long long n);
template <typename T>
T C(T n, T r);
void Calcfac(size_t size);
template <typename T>
T mod(T a, T b);
}  // namespace mystd
namespace mystd {
template <typename T>
static bool Input(int number, ...);
template <typename T>
static bool InputArray(std::vector<T> &array);
static bool InputArrays(long long number, ...);
static bool InputMatrix(std::vector<std::vector<long long>> array);
static long long min(std::vector<long long> array);
static long long max(std::vector<long long> array);
template <typename T>
static void Print(int number, ...);
template <typename T>
static void PrintArray(std::vector<T> array, const std::string sep);
};  // namespace mystd
template <typename T>
void mylist<T>::input() {
  mystd::InputArray<T>(list);
}
template <typename T>
void mylist<T>::sort() {
  std::sort(list.begin(), list.end());
};
template <typename T>
std::vector<size_t> mylist<T>::argsort() {
  std::vector<size_t> index(list.size());
  std::iota(index.begin(), index.end(), 0);
  std::sort(index.begin(), index.end(), [this](size_t i1, size_t i2) {
    return this->list[i1] < this->list[i2];
  });
  return index;
};
template <typename T>
int mylist<T>::find(T key) {
  typename std::vector<T>::iterator iter =
      std::find(list.begin(), list.end(), key);
  if (iter == list.end()) {
    return -1;
  } else {
    return std::distance(list.begin(), iter);
  }
}
template <typename T>
T mylist<T>::pop(size_t i) {
  T ans = list[i];
  list.erase(list.begin() + i);
  return ans;
}
template <typename T>
void mylist<T>::push(T value) {
  list.push_back(value);
}
template <typename T>
void mylist<T>::push(mylist<T> list_) {
  std::copy(list_.list.begin(), list_.list.end(),
            std::back_inserter(list_.list));
}
template <typename T>
mylist<T> mylist<T>::iloc(mylist<T> list_) {
  mylist<T> ans;
  for (auto &&i : list_.list) {
    ans.list.push_back(list[i]);
  }
  return ans;
}
template <typename T>
std::string mylist<T>::toString() {
  std::string string(list.begin(), list.end());
  return string;
}
template <typename T>
void mylist<T>::fromString(std::string string) {
  mylist<char> S;
  std::copy(string.begin(), string.end(), std::back_inserter(list));
}
template <typename T>
void mylist<T>::fromAlphabets(std::string string) {
  std::transform(string.begin(), string.end(), string.begin(), ::tolower);
  for (size_t i = 0; i < string.size(); i++) {
    typename std::vector<char>::iterator iter =
        std::find(alphabets.begin(), alphabets.end(), string[i]);
    list.push_back(std::distance(alphabets.begin(), iter));
  }
}
template <typename T>
std::string mylist<T>::toAlphabets(bool upper) {
  std::string alp;
  for (auto &&i : list) {
    alp.push_back(
        alphabets[i - std::floor(i / alphabets.size()) * alphabets.size()]);
  }
  if (upper) {
    std::transform(alp.begin(), alp.end(), alp.begin(), ::toupper);
  }
  return alp;
}
template <typename T>
template <typename V>
void mylist<T>::add(V value) {
  for (auto &&i : list) {
    i += value;
  }
}
template <typename T>
void mylist<T>::range() {
  std::iota(list.begin(), list.end(), 0);
}
template <typename T>
void mylist<T>::range(long long length) {
  list.resize(length);
  std::iota(list.begin(), list.end(), 0);
}
template <typename T>
void mylist<T>::range(long long start, long long end) {
  list.resize(end - start);
  std::iota(list.begin(), list.end(), start);
}
template <typename T>
size_t mylist<T>::min_index() {
  typename std::vector<T>::iterator iter =
      std::min_element(list.begin(), list.end());
  return std::distance(list.begin(), iter);
}
template <typename T>
T mylist<T>::min() {
  typename std::vector<T>::iterator iter =
      std::min_element(list.begin(), list.end());
  return list[std::distance(list.begin(), iter)];
}
template <typename T>
size_t mylist<T>::max_index() {
  typename std::vector<T>::iterator iter =
      std::max_element(list.begin(), list.end());
  return std::distance(list.begin(), iter);
}
template <typename T>
T mylist<T>::max() {
  typename std::vector<T>::iterator iter =
      std::max_element(list.begin(), list.end());
  return list[std::distance(list.begin(), iter)];
}
template <typename T>
T mystd::factorical(T a) {
  T ans = 1;
  for (size_t i = 0; i < a; i++) {
    ans *= i + 1;
  }
  return ans;
}
template <typename T>
T mystd::LCM(T a, T b) {
  return a * b / GCD(a, b);
}
template <typename T>
T mystd::GCD(T a, T b) {
  if (a < b) {
    T tmp = a;
    a = b;
    b = tmp;
  }
  T r = a % b;
  while (r != 0) {
    a = b;
    b = r;
    r = a % b;
  }
  return b;
}
template <typename T>
T mystd::LCM(std::vector<T> a) {
  if (a.size() < 1) {
    return 1;
  } else {
    T lcm = LCM(a[0], a[1]);
    for (size_t i = 1; i < a.size() - 1; i++) {
      T lcm_temp = LCM(lcm, a[i + 1]);
      if (lcm < lcm_temp) {
        lcm = lcm_temp;
      }
    }
    return lcm;
  }
}
template <typename T>
T mystd::LCM(mylist<T> a) {
  if (a.list.size() < 1) {
    return 1;
  } else {
    T lcm = LCM(a.list[0], a.list[1]);
    for (size_t i = 1; i < a.list.size() - 1; i++) {
      T lcm_temp = LCM(lcm, a.list[i + 1]);
      if (lcm < lcm_temp) {
        lcm = lcm_temp;
      }
    }
    return lcm;
  }
}
template <typename T>
T mystd::GCD(std::vector<T> a) {
  if (a.list.size() < 1) {
    return 1;
  } else {
    T gcd = GCD(a[0], a[1]);
    for (size_t i = 1; i < a.size() - 1; i++) {
      T gcd_temp = GCD(gcd, a[i + 1]);
      if (gcd < gcd_temp) {
        gcd = gcd_temp;
      }
    }
    return gcd;
  }
}
template <typename T>
T mystd::GCD(mylist<T> a) {
  if (a.list.size() < 1) {
    return 1;
  } else {
    T gcd = GCD(a.list[0], a.list[1]);
    for (size_t i = 1; i < a.list.size() - 1; i++) {
      T gcd_temp = GCD(gcd, a.list[i + 1]);
      if (gcd < gcd_temp) {
        gcd = gcd_temp;
      }
    }
    return gcd;
  }
}
long long mystd::pow(long long x, long long n) {
  long long ans = 1;
  while (n != 0) {
    if (n & 1) ans = ans * x % MOD;
    x = x * x % MOD;
    n = n >> 1;
  }
  return ans;
}
template <typename T>
T mystd::C(T n, T r) {
  if (!calcurated_fac) Calcfac(fac_size);
  if (n == 0 && r == 0) return 1;
  if (n < r || n < 0) return 0;
  T tmp = ifac[n - r] * ifac[r] % MOD;
  return tmp * fac[n] % MOD;
}
void mystd::Calcfac(size_t size) {
  fac.resize(size + 1);
  ifac.resize(size + 1);
  fac[0] = 1;
  ifac[0] = 1;
  for (long long i = 0; i < size; i++) {
    fac[i + 1] = fac[i] * (i + 1) % MOD;
    ifac[i + 1] = ifac[i] * pow(i + 1, MOD - 2) % MOD;
  }
  calcurated_fac = true;
}
template <typename T>
T mystd::mod(T a, T b) {
  return a - std::floor((long double)a / b) * b;
}
template <typename T>
bool mystd::Input(int number, ...) {
  va_list args;
  va_start(args, number);
  for (long long i = 0; i < number; i++) {
    std::cin >> *(va_arg(args, T *));
  }
  return true;
}
template <typename T>
void mystd::Print(int number, ...) {
  va_list args;
  va_start(args, number);
  for (long long i = 0; i < number; i++) {
    if (i != 0) {
      std::cout << " ";
    }
    std::cout << *(va_arg(args, T *));
  }
  std::cout << std::endl;
  ;
}
template <typename T>
void mystd::PrintArray(std::vector<T> array, const std::string sep) {
  for (long long i = 0; i < array.size(); i++) {
    if (i != 0) {
      std::cout << sep;
    }
    std::cout << array[i];
  }
  std::cout << std::endl;
  ;
}
template <typename T>
bool mystd::InputArray(std::vector<T> &array) {
  for (size_t i = 0; i < array.size(); i++) {
    std::cin >> array[i];
  }
  return true;
}
bool mystd::InputArrays(long long number, ...) {
  va_list args;
  va_start(args, number);
  std::vector<std::vector<long long> *> arrays(number);
  for (auto &i : arrays) {
    i = va_arg(args, std::vector<long long> *);
  }
  long long length = arrays[0]->size();
  for (long long j = 0; j < length; j++) {
    for (auto &&i : arrays) {
      std::cin >> (*i)[j];
    }
  }
  return true;
}
long long mystd::min(std::vector<long long> array) {
  long long ans = array[0];
  for (long long &i : array) {
    if (i < ans) {
      ans = i;
    }
  }
  return ans;
}
long long mystd::max(std::vector<long long> array) {
  long long ans = array[0];
  for (long long &i : array) {
    if (i > ans) {
      ans = i;
    }
  }
  return ans;
}
using namespace mystd;
void Main() {
  long long N;
  long long M;
  mystd::Input<long long>(2, &N, &M);
  bool ans = true;
  std::vector<int> A(N + 1, 0);
  A[1] = 1;
  std::vector<bool> C(N + 1, false);
  for (size_t i = 0; i < M; i++) {
    long long s, c;
    mystd::Input<long long>(2, &s, &c);
    if ((C[s] == true && A[s] != c) || (s == 1 && c == 0)) {
      ans = false;
    } else {
      A[s] = c;
      C[s] = true;
    }
  }
  if (ans) {
    for (size_t i = 1; i < N + 1; i++) {
      std::cout << A[i];
    }
    std::cout << std::endl;
  } else {
    std::cout << -1 << std::endl;
  }
}
int main(int argc, char const *argv[]) {
  Main();
  return 0;
}
