#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace __gnu_pbds;
using namespace std;
#ifdef ENABLE_DEBUG
#define dump(a) cerr<<#a<<"="<<a<<endl
#define dumparr(a,n) cerr<<#a<<"["<<n<<"]="<<a[n]<<endl
#else
#define dump(a) 
#define dumparr(a,n) 
#endif
#define FOR(i, a, b) for(ll i = a;i < b;i++)
#define For(i, a) FOR(i, 0, a)
#define REV(i, a, b) for(ll i = b-1;i >= a;i--)
#define Rev(i, a) REV(i, 0, a)
#define REP(a) For(i, a)
#define SIGN(a) (a==0?0:(a>0?1:-1))

typedef long long int ll;
typedef unsigned long long ull;
typedef unsigned int uint;
typedef pair<ll, ll> pll;
typedef pair<ll,pll> ppll;
typedef vector<ll> vll;
typedef long double ld;
typedef pair<ld,ld> pdd;

const ll INF=(1LL<<50);
#if __cplusplus<201700L
ll gcd(ll a, ll b) {
  if(a < b) return gcd(b, a);
  ll r;
  while ((r=a%b)) {
    a = b;
    b = r;
  }
  return b;
}
#endif
template<class T>
bool chmax(T& a,const T& b){
  if(a<b){
    a=b;
    return true;
  }
  return false;
}
template<class T>
bool chmin(T& a,const T& b){
  if(a>b){
    a=b;
    return true;
  }
  return false;
}
template<class S,class T>
std::ostream& operator<<(std::ostream& os,pair<S,T> a){
  os << "(" << a.first << "," << a.second << ")";
  return os;
}
template<class T>
std::ostream& operator<<(std::ostream& os,vector<T> a){
  os << "[ ";
  REP(a.size()){
    os<< a[i] << " ";
  }
  os<< " ]";
  return os;
}


void solve(long long N, long long M, std::vector<long long> s, std::vector<long long> c){
  vector<ll>ans(N,-1);
  REP(M){
    ll tmp=s[i]-1;
    if(ans[tmp]==-1||ans[tmp]==c[i])
      ans[s[i]-1]=c[i];
    else
    {
      cout<<-1<<endl;
      return;
    }
  }
  if(ans.front()==0){
    cout<<-1<<endl;
    return;
  }
  REP(N){
    if(ans[i]==-1){
      if(i==0){
        ans[i]=1;
      }else{
        ans[i]=0;
      }
    }
    cout<<ans[i];
  }
  cout<<endl;
}

int main(){
  cout<<setprecision(1000);
    long long N;
    scanf("%lld",&N);
    long long M;
    scanf("%lld",&M);
    std::vector<long long> s(M);
    std::vector<long long> c(M);
    for(int i = 0 ; i < M ; i++){
        scanf("%lld",&s[i]);
        scanf("%lld",&c[i]);
    }
    solve(N, M, std::move(s), std::move(c));
    return 0;
}
