#include <algorithm>
#include <complex>
#include <cstdlib>
#include <ctime>
#include <iomanip>
#include <iostream>
#include <map>
#include <math.h>
#include <queue>
#include <random>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <vector>

using namespace std;
#define SAY_YES cout << "YES" << endl;
#define SAY_Yes cout << "Yes" << endl;
#define SAY_NO cout << "NO" << endl;
#define SAY_No cout << "No" << endl;
#define IFYES(TRUE_OR_FALSE)   \
    if (TRUE_OR_FALSE)         \
    {                          \
        cout << "YES" << endl; \
    }                          \
    else                       \
    {                          \
        cout << "NO" << endl;  \
    }
#define IFYes(TRUE_OR_FALSE)   \
    if (TRUE_OR_FALSE)         \
    {                          \
        cout << "Yes" << endl; \
    }                          \
    else                       \
    {                          \
        cout << "No" << endl;  \
    }
#define IFyes(TRUE_OR_FALSE)   \
    if (TRUE_OR_FALSE)         \
    {                          \
        cout << "yes" << endl; \
    }                          \
    else                       \
    {                          \
        cout << "no" << endl;  \
    }
#define DEBUG_OUTPUT_ARRAY(XXX, ONE)                            \
    for (int i = 0; i < (ONE); i++)                             \
    {                                                           \
        cout << "DEBUG: i = " << i << " -> " << XXX[i] << endl; \
    }
#define DEBUG_OUTPUT_ARRAY2(XXX, ONE, TWO)                             \
    for (int i = 0; i < (ONE); i++)                                    \
    {                                                                  \
        cout << "<<< i = " << i << " >>>" << endl;                     \
        for (int j = 0; j < (TWO); j++)                                \
        {                                                              \
            cout << "DEBUG: j = " << j << " -> " << XXX[i][j] << endl; \
        }                                                              \
    }
#define DEBUG_OUTPUT_ARRAY2_BOX(XXX, ONE, TWO) \
    for (int i = 0; i < (ONE); i++)            \
    {                                          \
        cout << i << "  ";                     \
        for (int j = 0; j < (TWO); j++)        \
        {                                      \
            cout << XXX[i][j] << " ";          \
        }                                      \
        cout << endl;                          \
    }

typedef pair<long long int, long long int> pll;


const long long int mod = 1000000007;
const long long int INF = 99999999999999999;

long long int N,M,Q,A[255][255],b[20],sum=0,res=0,sta=1,s[10],c[10];

int main()
{
    cout << fixed << setprecision(18);
	
	cin>>N>>M;
	for(int i=1;i<N;i++){
		sta*=10;
	}
	for(int i=0;i<M;i++){
		cin>>s[i]>>c[i];
	}
	if(N==3){
		for(int i=100;i<1000;i++){
			bool key=true;
			for(int j=0;j<M;j++){
				if(s[j]==1){
					if(i/100!=c[j]){key=false;}
				}else if(s[j]==2){
					if((i%100)/10!=c[j]){key=false;}
				}else{
					if(i%10!=c[j]){key=false;}
				}
			}
			if(key){cout<<i<<endl;return 0;}
		}
	}else if(N==2){
		for(int i=10;i<100;i++){
			bool key=true;
			for(int j=0;j<M;j++){
				if(s[j]==1){
					if(i/10!=c[j]){key=false;}
				}else if(s[j]==2){
					if(i%10!=c[j]){key=false;}
				}
				
			}
			if(key){cout<<i<<endl;return 0;}
		}
	}else{
		for(int i=0;i<10;i++){
			bool key=true;
			for(int j=0;j<M;j++){
				if(s[j]==1){
					if(i%10!=c[j]){key=false;}
				}
				
			}
			if(key){cout<<i<<endl;return 0;}
		}
	}
	cout<<-1<<endl;
}



Measured memory_bytes: 256