#include <bits/stdc++.h>
using namespace std;
template <class T>
void chmax(T& a, T b) {
  if (a < b) a = b;
}
template <class T>
void chmin(T& a, T b) {
  if (a > b) a = b;
}
constexpr long long INF = 1000000000000000000;
constexpr long long mod = 1000000007;
long long dx[] = {0, 1, 0, -1}, dy[] = {1, 0, -1, 0};
long long kaijo[2000010];
struct edge {
  long long to, cost;
};
long long gcd(long long a, long long b) {
  if (b == 0) return a;
  return gcd(b, a % b);
}
long long lcm(long long a, long long b) { return a / gcd(a, b) * b; }
bool prime(long long a) {
  if (a == 1) return false;
  for (long long i = 2; i * i <= a; i++) {
    if (a % i == 0) return false;
  }
  return true;
}
void init_fact() {
  kaijo[0] = 1;
  for (long long i = 1; i <= 2000000; i++) {
    kaijo[i] = kaijo[i - 1] * i;
    kaijo[i] %= mod;
  }
}
long long modpow(long long a, long long b) {
  if (b == 0) return 1;
  if (b % 2) return modpow(a, b - 1) * a % mod;
  long long memo = modpow(a, b / 2);
  return memo * memo % mod;
}
long long comb(long long a, long long b) {
  if (!kaijo[0]) init_fact();
  return kaijo[a] * modpow(kaijo[a - b], mod - 2) % mod *
         modpow(kaijo[b], mod - 2) % mod;
}
long long inv(long long x) {
  x = modpow(x, mod - 2);
  return x;
}
bool kosa(double ax, double ay, double bx, double by, double cx, double cy,
          double dx, double dy) {
  double ta = (cx - dx) * (ay - cy) + (cy - dy) * (cx - ax);
  double tb = (cx - dx) * (by - cy) + (cy - dy) * (cx - bx);
  double tc = (ax - bx) * (cy - ay) + (ay - by) * (ax - cx);
  double td = (ax - bx) * (dy - ay) + (ay - by) * (ax - dx);
  return tc * td < 0 && ta * tb < 0;
}
double dist(double ax, double ay, double bx, double by) {
  return sqrt((bx - ax) * (bx - ax) + (ay - by) * (ay - by));
}
long long n, m, s[10], c[10], num[10];
signed main() {
  cin >> n >> m;
  fill(num, num + 10, -1);
  for (long long i = 0; i < m; i++) {
    cin >> s[i] >> c[i];
    if (num[s[i]] != -1 && num[s[i]] != c[i]) {
      puts("-1");
      return 0;
    }
    num[s[i]] = c[i];
  }
  if (num[1] == 0 && n != 1) {
    puts("-1");
    return 0;
  }
  for (long long i = 1; i <= n; i++) {
    if (num[i] == -1) {
      if (i == 1)
        num[i] = 1;
      else
        num[i] = 0;
    }
    cout << num[i];
  }
  cout << endl;
  return 0;
}
