#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp> 
#include <ext/pb_ds/detail/standard_policies.hpp>
#include <ext/rope>

using namespace std;
using namespace __gnu_pbds;
using namespace __gnu_cxx;

#define IOS ios::sync_with_stdio(0); cin.tie(0); cout.tie(0);
#define endl "\n"
#define long long long 
#define PI 3.141592653589793238

#pragma GCC target ("avx2")
#pragma GCC optimization ("O3")
#pragma GCC optimization ("unroll-loops")

#define TRACE
#ifdef TRACE
#define trace(...) __f(#__VA_ARGS__, __VA_ARGS__)
    template <typename Arg1>
    void __f(const char* name, Arg1&& arg1){
        cout << name << " : " << arg1 << endl;
        //use cerr if u want to display at the bottom
    }
    template <typename Arg1, typename... Args>
    void __f(const char* names, Arg1&& arg1, Args&&... args){
        const char* comma = strchr(names + 1, ','); cout.write(names, comma - names) << " : " << arg1<<" | ";__f(comma+1, args...);
    }
#else
#define trace(...)
#endif

typedef trie<string,null_type,trie_string_access_traits<>,pat_trie_tag,trie_prefix_search_node_update> pref_trie;
typedef tree<long int,null_type,less<long int>,rb_tree_tag,tree_order_statistics_node_update>ordered_set;
typedef cc_hash_table<long int,long int, hash<long int>, equal_to<long int>, direct_mask_range_hashing<long int>, 
hash_standard_resize_policy<hash_exponential_size_policy<>, hash_load_check_resize_trigger<true>, true>> ht;
typedef gp_hash_table<long int,long int> HashTable;

int main(){
   IOS;
 /*    #ifndef ONLINE_JUDGE
         freopen("in.txt",  "r",  stdin);
         freopen("out.txt", "w", stdout);
     #endif */
   
   long int n,m;
   cin>>n>>m;

   vector<long int> v(n,-1);

   while(m--){
      long int x,y;
      cin>>x>>y;
      x--;

      if(v[x] != -1 && v[x] != y)
        return cout<<"-1",0;

      if(x == 0 && y == 0 && n > 1)
        return cout<<"-1",0;

      v[x] = y;
   }

   if(v[0] == -1)
      v[0] = 1;

   for(long int i = 0; i < n; i++)
      if(v[i] != -1)
        cout<<v[i];
      else
        cout<<"0";

   return 0;
}