#include <bits/stdc++.h>
using namespace std;

#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace __gnu_pbds;

#define fast ios_base::sync_with_stdio(0);cin.tie(NULL);cout.tie(NULL)

#define ordered_set tree<int, null_type,less<int>, rb_tree_tag,tree_order_statistics_node_update>

#define ll long long
#define ld long double
#define pb(a) push_back(a)
#define eb(a) emplace_back(a)

#define xx first
#define yy second
#define mp make_pair
#define pll pair<ll,ll>
#define mll map<ll,ll>
#define vll vector<ll>
#define pdd pair<double,double>
#define ALL(v) (v).begin(), (v).end()

const ll MOD=1e9+7; ;
const ll inf=1e18;

#define MODSET(d) if ((d) >= MOD) d %= MOD;
#define MODNEGSET(d) if ((d) < 0) d = ((d % MOD) + MOD) % MOD;
#define put(x) cout<<#x<<" = "<<x<<endl;

ll power(ll a,ll n){
    ll ans=1;
    while(n){
        if(n&1)
            ans=(ans*a);
        n>>=1;
        a=(a*a);
    }
    return ans;
}


ll powerMod(ll a,ll n){
    ll ans=1;
    while(n){
        if(n&1)
            ans=(ans*a)%MOD;
        n/=2;
        a=(a*a)%MOD;
    }
    return ans;
}

ll powerMod1(ll a,ll n,ll mod){
    ll ans=1;
    while(n){
        if(n&1)
            ans=(ans*a)%mod;
        n>>=1;
        a=(a*a)%mod;
    }
    return ans;
}

ll lcm(ll a,ll b){
    return a*(b/__gcd(a,b));
}

ll sumdigit(ll n){
    ll sum=0;
    while(n){
        sum+=n%10;
        n=n/10;
    }
    return sum;
}

ll countSetBit(ll a){
    return __builtin_popcount(a);
}
ll countBit(ll a){
    ll sum=0;
    while(a){
        sum++;
        a>>=1;
    }
    return sum;
}

ll length(ll a){
    ll ans=0;
    while(a){
        ans++;
        a=a/10;
    }
    return ans;
}

bool isVowel(char c){
	if(c=='a' or c=='e' or c=='i' or c=='o' or c=='u')
		return true;
	return false;
}


int main()
{
    fast;
    ll t;
    //~ cin>>t;
    t=1;
    while(t--){
			ll n,m;
			cin>>n>>m;
			bool yeah=true;
			string s;
			map<int,int>mp;
			for(int i=0;i<n;i++){
				s+="0";
			}
			for(int i=0;i<m;i++){
				int k,c;
				cin>>k>>c;
				if(k==1 and c==0 and n>1){
					yeah=false;
				}else if(mp[k-1]==0){
					mp[k-1]++;
					s[k-1]=(char)(c+'0');
				}else if(mp[k-1]){
					if(s[k-1]-'0'!=c){
						yeah=false;
					}
				}
			}
			if(yeah){
				if(s[0]=='0')
					s[0]='1';
				cout<<s;
			}else cout<<-1;
    }
    return 0;
}
