#include<iostream>

using namespace std;
int main(){
int N,M,s[5],c[5],i,a=0;
int X[4];
X[1]=-1;
X[2]=-1;
X[3]=-1;

cin >> N >> M;
for(i=1;i<=M;i++){cin >> s[i] >> c[i];}

for(i=1;i<=M;i++){if((X[s[i]]==-1)||(X[s[i]]==c[i])){X[s[i]]=c[i];}else{a--;
break;}
    if(s[i]==1&&c[i]==0&&N!=1){a--;}
}
if(a==0){for(i=1;i<=N;i++){
if(i==1&&X[i]==-1&&N!=1){X[i]=1;}
if(i==1&&X[i]==-1&&N==1){X[i]=0;}
if((i==2||i==3)&&X[i]==-1){X[i]=0;}
}
}
if(a<0){cout << "-1";}else{
for(i=1;i<=N;i++){cout << X[i];}}
cout << endl;
return 0;
}