#include <bits/stdc++.h>
using namespace std;
const int fx[] = {+1, -1, +0, +0};
const int fy[] = {+0, +0, +1, -1};
const int fx8[] = {+0, +0, +1, -1, -1, +1, -1, +1};
const int fy8[] = {-1, +1, +0, +0, +1, +1, -1, -1};
const int kx[] = {-2, -2, -1, -1, 1, 1, 2, 2};
const int ky[] = {-1, 1, -2, 2, -2, 2, -1, 1};
int Set(int N, int pos) { return N = N | (1 << pos); }
int reset(int N, int pos) { return N = N & ~(1 << pos); }
bool check(int N, int pos) { return (bool)(N & (1 << pos)); }
void __print(int x) { cerr << x; }
void __print(long x) { cerr << x; }
void __print(long long x) { cerr << x; }
void __print(unsigned x) { cerr << x; }
void __print(unsigned long x) { cerr << x; }
void __print(unsigned long long x) { cerr << x; }
void __print(float x) { cerr << x; }
void __print(double x) { cerr << x; }
void __print(long double x) { cerr << x; }
void __print(char x) { cerr << '\'' << x << '\''; }
void __print(const char *x) { cerr << '\"' << x << '\"'; }
void __print(const string &x) { cerr << '\"' << x << '\"'; }
void __print(bool x) { cerr << (x ? "true" : "false"); }
template <typename T, typename V>
void __print(const pair<T, V> &x) {
  cerr << '{';
  __print(x.first);
  cerr << ',';
  __print(x.second);
  cerr << '}';
}
template <typename T>
void __print(const T &x) {
  int f = 0;
  cerr << '{';
  for (auto &i : x) cerr << (f++ ? "," : ""), __print(i);
  cerr << "}";
}
void _print() { cerr << "]\n"; }
template <typename T, typename... V>
void _print(T t, V... v) {
  __print(t);
  if (sizeof...(v)) cerr << ", ";
  _print(v...);
}
int main(void) {
  int n;
  cin >> n;
  int m;
  cin >> m;
  vector<int> a(n);
  for (int i = 0; i < m; i++) {
    int x, y;
    cin >> x >> y;
    x--;
    a[x] = y;
  }
  if (a[0] == 0) {
    cout << -1 << endl;
    return 0;
  }
  for (int i = 0; i < n; i++) cout << a[i];
  cout << endl;
  return 0;
}
