#include <bits/stdc++.h>
using namespace std;
constexpr long long int INFLL = 1001001001001001LL;
constexpr long long int infll = 1001001001001001LL;
constexpr int INF = 1000000007;
constexpr int inf = 1000000007;
const int mod = 1000000007;
template <class T>
inline bool chmin(T &a, T b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}
template <class T>
inline bool chmax(T &a, T b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}
long long gcd(long long a, long long b) {
  if (a % b == 0) {
    return (b);
  } else {
    return (gcd(b, a % b));
  }
}
long long lcm(long long a, long long b) { return a / gcd(a, b) * b; }
inline double nCr(const int n, int r) {
  if (n == 0) {
    return 0;
  }
  if (r == 0) {
    return 1;
  }
  if (r == 1) {
    return n;
  }
  if (n == r) {
    return 1;
  }
  if (r > n / 2) {
    r = n / 2;
  }
  double result = 1;
  for (double i = 1; i <= r; i++) {
    result *= (n - i + 1) / i;
  }
  return (result);
}
template <typename T>
T seinomi(T a) {
  if (a > 0) {
    return a;
  } else {
    return 0;
  }
}
template <typename T>
map<T, T> soinsuubunkai(T n) {
  map<T, T> ret;
  for (T i = 2; i * i <= n; i++) {
    while (n % i == 0) {
      ret[i]++;
      n /= i;
    }
  }
  if (n != 1) ret[n] = 1;
  return ret;
}
template <typename T>
T ketasuu(T num) {
  return std::to_string(num).length();
}
int kaizyou(int k) {
  int sum = 1;
  for (int i = 1; i <= k; ++i) {
    sum *= i;
  }
  return sum;
}
template <class ForwardIt, class T>
void iota(ForwardIt first, ForwardIt last, T value) {
  while (first != last) {
    *first++ = value;
    ++value;
  }
}
int factorial(int n) {
  int answer = 1;
  while (n > 1) {
    answer *= n;
    n--;
  }
  return answer;
}
int comb(int n, int r) {
  return factorial(n) / (factorial(r) * factorial(n - r));
}
long long modpow(long long a, long long n, long long mod) {
  long long res = 1;
  while (n > 0) {
    if (n & 1) res = res * a % mod;
    a = a * a % mod;
    n >>= 1;
  }
  return res;
}
int main() {
  long long n, m;
  cin >> n >> m;
  long long s, c;
  set<long long> s1, s2, s3;
  for (int i = 0; i < m; i++) {
    cin >> s >> c;
    if (s == 1) {
      s1.insert(c);
    } else if (s == 2) {
      s2.insert(c);
    } else if (s == 3) {
      s3.insert(c);
    }
  }
  if (s1.size() > 1 || s2.size() > 1 || s3.size() > 1) {
    cout << "-1" << endl;
  } else if (n > 1 && *s1.begin() == 0) {
    cout << "-1" << endl;
  } else {
    if (n == 3) {
      if (s1.size() == 0) {
        cout << "1";
      } else {
        cout << *s1.begin();
      }
      if (s2.size() == 0) {
        cout << "0";
      } else {
        cout << *s2.begin();
      }
      if (s3.size() == 0) {
        cout << "0";
      } else {
        cout << *s3.begin();
      }
    } else if (n == 2) {
      if (s1.size() == 0) {
        cout << "1";
      } else {
        cout << *s1.begin();
      }
      if (s2.size() == 0) {
        cout << "0";
      } else {
        cout << *s2.begin();
      }
    } else {
      if (s1.size() == 0) {
        cout << "0";
      } else {
        cout << *s1.begin();
      }
    }
  }
}
