//  Created by conan1024hao in 2020.
//  Copyright © 2020 conan1024hao. All rights reserved.
//  専用ライブラリです、自由にコピーして構いません。
//  感谢看我的代码！Wechat:conan1024hao Twitter/QQ:810396815
#pragma GCC optimize ("O3")
#include <iostream>
#include <iomanip>
#include <istream>
#include <ostream>
#include <sstream>
#include <iterator>
#include <vector>
#include <algorithm>
#include <queue>
#include <deque>
#include <list>
#include <stack>
#include <map>
#include <unordered_map>
#include <set>
#include <utility>
#include <cmath>
#include <cstdio>
#include <cstring>
#include <string>
#include <ctime>
#include <cctype>
#include <cstdlib>
#define IINF 10e8
#define INF 10e17
#define MOD 1000000007
#define mod 1000000007
#define rep(i, a, n) for (ll i = a; i < (ll)(n); i++)
#define Endl endl
#define fi first
#define se second
#define pb push_back
#define mp make_pair
#define eb emplace_back
#define mmax(x,y)(x>y?x:y)
#define mmin(x,y)(x<y?x:y)
#define chmax(x,y) x=mmax(x,y)
#define chmin(x,y) x=mmin(x,y)
#define all(x) (x).begin(),(x).end()
#define siz(x) (ll)(x).size()
#define PI acos(-1.0)
using namespace std;
//using Int=int_fast64_t;
typedef long long int ll;
typedef long long int LL;
typedef pair<ll,ll>Pll;
typedef pair<int,int>Pin;
template<class T> using V=vector<T>;
long long GCD(long long a, long long b) { return b ? GCD(b, a%b) : a; }
long long LCM(long long a, long long b)  {return a/GCD(a,b)*b;}
int dx[4]={-1,0,1,0};
int dy[4]={0,-1,0,1};
int ddx[8]={-1,0,1,0,1,1,-1,-1};
int ddy[8]={0,-1,0,1,1,-1,1,-1};
char dir[4]={'u','l','d','r'};
ll cmp(pair<ll,ll>a,pair<ll,ll> b){
        if(a.fi!=b.fi)
        return a.fi<b.fi;
        else
        return a.se<b.se;
}
//---------------------------------------------------------------------------
struct mint{
    using ull=unsigned long long int;
    ull v;
    mint(ll vv=0){s(vv%mod+mod);}
    mint& s(ull vv){
        v=vv<mod?vv:vv-mod;
        return *this;
    }
    //オーバーロード
    mint operator-()const{return mint()-*this;}//符号反転
    mint&operator+=(const mint&val){return s(v+val.v);}
    mint&operator-=(const mint&val){return s(v+mod-val.v);}
    mint&operator*=(const mint&val){
        v=ull(v)*val.v%mod;
        return *this;
    }
    mint&operator/=(const mint&val){return *this*=val.inv();}
    mint operator+(const mint&val){return mint(*this)+=val;}
    mint operator-(const mint&val){return mint(*this)-=val;}
    mint operator*(const mint&val){return mint(*this)*=val;}
    mint operator/(const mint&val){return mint(*this)/=val;}
    mint pow(int n)const{
        mint res(1),x(*this);
        while(n){
            if(n&1)res*=x;
            x*=x;
            n>>=1;
        }
        return res;
    }
    mint inv()const{return pow(mod-2);}
    //拡張ユークリッドの互除法
    /* mint inv()const{
        int x,y;
        int g=extgcd(v,mod,x,y);
        assert(g==1);
        if(x<0)x+=mod;
        return mint(x);
    }*/
    friend ostream& operator<<(ostream&os,const mint&val){
        return os<<val.v;
    }//出力
    bool operator<(const mint&val)const{return v<val.v;}
    bool operator==(const mint&val)const{return v==val.v;}
    bool operator>(const mint&val)const{return v>val.v;}
};
const ll MAX = 2000010;//設定
mint fac[MAX], finv[MAX], inv[MAX];
// テーブルを作る前処理
void init(){
    fac[0] = fac[1] = 1;
    for(int i=1;i<MAX;i++)fac[i]=fac[i-1]*i;
    finv[MAX-1]=fac[MAX-1].inv();
    for(int i=MAX-2;i>=0;i--)finv[i]=finv[i+1]*(i+1);
    for(int i=MAX-2;i>=1;i--)inv[i]=finv[i]+fac[i-1];
}
//階乗
mint factor(ll n,ll k){
  if (n<k) return 0;
  if (n<0 || k<0) return 0;
  return fac[n]*finv[k];
}
// 二項係数計算
mint COM(ll n, ll k){
    if (n < k) return 0;
    if (n < 0 || k < 0) return 0;
    return fac[n] * finv[k] * finv[n - k];
}
ll modpow(ll a, ll n) {//a^n(MOD)を求める
    ll res = 1;
    while (n > 0) {
        if (n & 1) res = res * a % MOD;
        a = a * a % MOD;//次の準備
        n >>= 1;
    }
    return res;
}
ll waru(ll a,ll b){
    return a*modpow(b,MOD-2)%MOD;
}

ll permutation(ll n,ll r)
{
    ll a=1;
    for(ll i=n-r+1;i<=n;i++)
        a*=i;
    return a;
}


//---------------------------------------------------------------------------
int main(){//問題をちゃんと見ろ! llか? 统一类型 memset()! ペナを減らせ!!!!!!!!!!!!!
    cin.tie(0);
    ios::sync_with_stdio(false);
    //-------------------------------
    int n,m;cin>>n>>m;
    vector<int>s(m),c(m);
    for(int i=0;i<m;i++){
        cin>>s[i]>>c[i];
        if(n==1){
            s[i]=2;
        }
        else if(n==3){
            s[i]--;
        }
    }
    int ans[3];
    for(int i=0;i<3;i++)ans[i]=-1;
    for(int i=0;i<m;i++){
        if(ans[s[i]]==-1){
            ans[s[i]]=c[i];
            if(c[i]==0&&n==2&&s[i]==1){
                cout<<-1<<endl;
                return 0;
            }
            else if(c[i]==0&&n==3&&s[i]==0){
                cout<<-1<<endl;
                return 0;
            }
        }
        else{
            if(c[i]!=ans[s[i]]){
                cout<<-1<<endl;
                return 0;
            }
        }
    }
    if(n==1){
        if(ans[2]==-1)ans[2]=0;
        cout<<ans[2]<<endl;
    }
    else if(n==2){
        if(ans[2]==-1)ans[2]=0;
        if(ans[1]==-1)ans[1]=1;
        cout<<ans[1]<<ans[2]<<endl;
    }
    else{
        if(ans[2]==-1)ans[2]=0;
        if(ans[1]==-1)ans[1]=0;
        if(ans[0]==-1)ans[0]=1;
        cout<<ans[0]<<ans[1]<<ans[2]<<Endl;
    }
    //------------------------------
    return 0;
}
//---------------------------------------------------------------------------
/*
int n;cin>>n;
vector<int>a(n);
for(int i=0;i<n;i++)
    cin>>a[i];
 */


Measured memory_bytes: 47104