#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
 
#define int long long
#define ull unsigned long long
#define ld long double
#define rep(a) rep1(i,a)
#define rep1(i,a) rep2(i,0,a)
#define rep2(i,b,a) for(int i=(b); i<((int)(a)); i++)
#define rep3(i,b,a) for(int i=(b); i>=((int)(a)); i--)
#define all(a) a.begin(),a.end()
#define pii pair<int,int>
#define pb push_back
#define mp make_pair
#define sz(a) ((int)a.size())
#define pow2(x) (1ll<<(x))
#define print0(a) cout << (a) << ' '
#define print1(a) cout << (a) << '\n'
#define print2(a,b) cout << (a) << ' ',print1(b)
#define print3(a,b,c) cout << (a) << ' ',print2(b,c)
#define print4(a,b,c,d) cout << (a) << ' ',print3(b,c,d)
#ifdef i_am_noob
#define debug(a) print2(#a,a)
#else
#define debug(a) 
#endif
#define ordered_set tree<int,null_type,less<int>,rb_tree_tag,tree_order_statistics_node_update>
 
using namespace std;
using namespace __gnu_pbds;
 
const int Mod=1000000007,Mod2=998244353;
const int MOD=Mod2;
 
inline int add(int a, int b){return (a+b>=MOD?a+b-MOD:a+b);}
inline int sub(int a, int b){return (a+MOD-b>=MOD?a-b:a+MOD-b);}
int Pow(int a, int b){
	if(!b) return 1;
	int tmp=Pow(a*a%MOD,b>>1);
	return (b&1?tmp*a%MOD:tmp);
}
inline int inverse(int n){return Pow(n,MOD-2);}
 
const int maxn=200005;
//i_am_noob
int n,m,x,y,ans[3];

signed main(){
	ios_base::sync_with_stdio(0),cin.tie(0);
	cin >> n >> m;
	rep(3) ans[i]=-1;
	rep(m){
		cin >> x >> y;
		x--;
		if(n>1&&x==0&&y==0){
			print1(-1);
			return 0;
		}
		if(ans[x]==-1) ans[x]=y;
		if(ans[x]!=y){
			print1(-1);
			return 0;
		}
	}
	rep(n) if(ans[i]==-1) ans[i]=i==0?1:0;
	rep(n) cout << ans[i];
	cout << '\n';
	return 0;
}
