//#include<bits/stdc++.h>
#include<cstdio>
#include<iostream>
#include<algorithm>
#include<cstring>
#include<cmath>
#include<map>
#include<queue>
#include<stack>
#include<set>
#include<unordered_map>
#include<bitset>
using namespace std;
#define int long long
#define ll long long
#define str string
#define db double
#define ac() cout<<"Yes"<<endl
#define wa()  cout<<"No"<<endl
#define ddd cout<<"---debug---"<<endl;
#define ff(a,b) for(signed long long (a)=1;(a)<=(b);(a)++)
#define fff(a,b) for(signed long long (a)=0;(a)<(b);(a)++)
#define re readdd()
#define pr(a) printtt(a)
#define pee puts("");
#define eee putchar(' ');
#define pss(a) push_back(a)
#define ps(a) push(a)
#define SZ(x) x.size()
#define epp empty()
#define all(x) x.begin(),x.end()
typedef vector<int> VE;
int gcd(int a,int b){return b==0?a:gcd(b,a%b);}//
int ppow(int a,int b,int mod){a%=mod;//
int ans=1%mod;while(b){if(b&1)ans=(long long)ans*a%mod;
a=(long long)a*a%mod;b>>=1;}return ans;}
int readdd(){int x=0,f=1;char c=getchar();//
while(!isdigit(c)&&c!='-')c=getchar();
if(c=='-')f=-1,c=getchar();
while(isdigit(c))x=x*10+c-'0',c=getchar();
return f*x;}
void printtt(int x){if(x<0)putchar('-'),x=-x;
if(x>=10)printtt(x/10);putchar(x%10+'0');}
bool addd(int a,int b){return a>b;};
//
const int maxm=1e5+5;
int a[maxm];
signed main(){
    memset(a,-1,sizeof a);
    int n=re,m=re;
    ff(mm,m){
        int x=re,xx=re;
        if(a[x]!=-1&&a[x]!=xx){
            puts("-1");return ;
        }
        a[x]=xx;
    }
    if(a[1]==-1)a[1]=1;
    ff(i,n){
        if(a[i]==-1)a[i]=0;
    }
    ff(i,n)pr(a[i]);
    return 0;
}
