/*

PAIN demands to be felt
so do RE, TLE, MLE, SIGSEV & WA

*/

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

// -----------------<fast IO>------------------
#define CIN 			ios::sync_with_stdio(0); cin.tie(0); cout.tie(0);
#define FLSH 			fflush(stdout)
#define fileIO(name) \
    freopen(name".in", "r", stdin); \
    freopen(name".out", "w", stdout);
#define PRECISION(x) 	cout << fixed << setprecision(x);
#define endl 			"\n"
// -----------------<Hardware instructions>------------------
#define onecount        __builtin_popcount
// -----------------<Container manipulation / traversal macros>------------------
#define mp 				make_pair
#define pb	 			push_back
#define ff 				first
#define ss 				second
#define sz(x) 			((int)((x).size()))
#define all(x) 			(x).begin(),(x).end()
#define rep(i,n) 		for(int (i)=0;(i)<(n);(i)++)
#define forn(i,a,b) 	for(int (i)=(a);(i)<=(b);(i)++)
#define fill(l,a)		memset((l) , (a) , sizeof(l))
// -----------------<Some common useful functions>------------------
#define maX(a,b)		( (a) > (b) ? (a) : (b))
#define miN(a,b)        ( (a) < (b) ? (a) : (b))
#define checkbit(n,b)   ( (n >> b) & 1)
#define INDEX(arr,i)  	( lower_bound(all(arr),i)-arr.begin())
#define in(b,a)         ( (b).find(a) != (b).end())
// -----------------<TypeDef Start>------------------
typedef long double ld;
typedef long long ll;
typedef unsigned long long ull;
typedef pair<ll, ll> pii;
typedef vector<ll> vi;
typedef vector< std::vector<ll> > matrix;
typedef map<ll,ll> mii;
typedef vector<pii> vpii;
// -----------------<Constants>------------------
const int MAXN = 1000005;
const int SQRTN = 1003;
const int LOGN = 22;
const double PI=acos(-1);

const int INF=1e9;

const int MOD = 1000000007;
const int FMOD = 998244353;
const double eps = 1e-9;
// -----------------<Modular Arithmetic>------------------
template<typename T> T gcd(T a, T b)
	{return(b?__gcd(a,b):a);}
template<typename T> T lcm(T a, T b)
	{return(a*(b/gcd(a,b)));}
template<typename T> T add(T a, T b, T c = MOD)
	{T res=a+b;return(res>=c?res-c:res);}
template<typename T> T mod_neg(T a, T b, T c = MOD)
	{T res;if(abs(a-b)<c)res=a-b;else res=(a-b)%c;return(res<0?res+c:res);}
template<typename T> T mul(T a, T b, T c = MOD)
	{ll res=(ll)a*b;return(res>=c?res%c:res);}
inline ll mulmod(ll a,ll b, ll m = MOD)
	{ll q = (ll)(((ld)a*(ld)b)/(ld)m);ll r=a*b-q*m;if(r>m)r%=m;if(r<0)r+=m;return r;}
template<typename T>T expo(T e, T n)
	{T x=1,p=e;while(n){if(n&1)x=x*p;p=p*p;n>>=1;}return x;}
template<typename T>T power(T e, T n, T m = MOD)
	{T x=1,p=e;while(n){if(n&1)x=mul(x,p,m);p=mul(p,p,m);n>>=1;}return x;}
template<typename T>T extended_euclid(T a, T b, T &x, T &y)
	{T xx=0,yy=1;y=0;x=1;while(b){T q=a/b,t=b;b=a%b;a=t;t=xx;xx=x-q*xx;x=t;t=yy;yy=y-q*yy;y=t;}return a;}
template<typename T>T mod_inverse(T a, T n = MOD)
	{T x,y,z=0;T d=extended_euclid(a,n,x,y);return(d>1?-1:mod_neg(x,z,n));}
// --------------------------------------------------</TEMPLATE>--------------------------------------------------

void solve(){
	ll n=0, x=0, m=0, curr=0, num=0, n1=0, n2=0, n3=0, n4=0, i=0 , j=0;
	ll root=0, sum=0, diff=0, q=0, choice=0, d=0, len=0, beg=0, end=0, pos=0, cnt=0;
	ll lo=0, hi=0, mid=0, ans=0;
	bool flag = false;
	string s1, s2, s3, str;
	char ch, ch1, ch2, ch3, *ptr;
	double dub=0;
	/////////////////////////////////////////////////////////////////////////////////////////////////////////////
	cin>>n>>m;
	ll s[m],c[m];
	ll dig[n+1];
	rep(i,n+1){
		dig[i]=-1;
	}
	rep(i,m){
		cin>>s[i]>>c[i];
		if(dig[s[i]]==-1){
			dig[s[i]]=c[i];
		}
		else{
			if(dig[s[i]]!=c[i]){
				flag=false;
				cout<<-1<<endl;
				return;
			}
		}
	}
	if(dig[1]==0&&n>1)cout<<-1<<endl;
	else{
		rep(i,n){
			if(dig[i+1]!=-1)
			cout<<dig[i+1];
			else if(i>0) cout<<0;
			else if(n>1) cout<<1;
			else cout<<0;
		}
	}
}

int main(){

	int t=1;
	//cin>>t;
	while(t--){
		solve();
	}

	return 0;
}





Measured memory_bytes: 256