//
import java.math.*;
import java.util.*;
import java.io.*;
  
public class Main { 
  
    static BufferedReader in;
    static PrintWriter out = new PrintWriter(System.out);
    static String file = "../in";
    static int test = 10; // 0 for local testing, 1 for std input
    static int inf = 1_000_000, mod = 1_000_000_007;

    void swap(int[]ary, int i, int j)
    {
        int t = ary[i];
        ary[i] = ary[j];
        ary[j] = t;
    }
    
    String[] split() throws Exception
    {
        return in.readLine().split(" ");
    }

    int readInt() throws Exception
    {
        return Integer.valueOf(in.readLine());
    }

    int[] toIntArray() throws Exception
    {
        String[] sp = split();
        int n = sp.length;
        int[] ary = new int[n];
        for(int i = 0; i < n; i++) ary[i] = Integer.valueOf(sp[i]);
        return ary;
    }

    String reverse(String str)
    {
        return new StringBuilder(str).reverse().toString();
    }


    long pow(long a, int pow)
    {
        long res = 1;
        while(pow > 0)
        {
            if(pow % 2 != 0) {
                res *= a;
                res %= mod;
            }
            a = a * a;
            a %= mod;
            pow /= 2;
        }

        return res;
    }

    public static void main(String[] args) throws Exception
    {
        int _k = Integer.valueOf("1");
        if(test > 0) in = new BufferedReader(new InputStreamReader(System.in));
        else in = new BufferedReader(new FileReader(file));
        if(test < 0) {String[] str = in.readLine().split(" ");}
/***********************************************************************/
/***********************************************************************/
/***********************************************************************/
/***********************************************************************/
        // System.out.println((-100 + 0) / 2);

        new Main().c();
        out.flush();
    }

    void c() throws Exception
    {
        int[] ary = toIntArray();
        int n = ary[0], m = ary[1];

        int[] digits = new int[n];
        Arrays.fill(digits, -1);
        int[] vis = new int[n];
        while(m-- > 0)
        {
            ary = toIntArray();
            int s = ary[0] - 1, c = ary[1];
            if(digits[s] > 0 && digits[s] != c)
            {
                out.println(-1);
                return;
            }
            // vis[s]++;
            digits[s] = c;
        }
        if(digits[0] == 0 && n > 1)
        {
            out.println(-1);
            return;
        }
        for(int i = 0; i < n; i++)
        {
            if(digits[i] < 0) digits[i] = 0;
        }
        if(digits[0] == 0 && n > 1) digits[0] = 1;
        for(int k : digits) out.printf("%d", k);

    }
    void b() throws Exception
    {
        int[][] g = new int[3][];
        for(int i = 0; i < 3; i++)
        {
            g[i] = toIntArray();
        }
        int n = readInt();
        boolean[][] v = new boolean[3][3];
        while(n-- > 0)
        {
            int b = readInt();
            for(int i = 0; i < 3; i++)
            {
                for(int j = 0; j < 3; j++)
                {
                    if(g[i][j] == b) v[i][j] = true;
                }
            }
        }

        boolean ans = false;
        for(int i = 0; i < 3; i++)
        {
            boolean col = true;
            for(int j = 0; j < 3; j++)
            {
                col &= v[i][j];
            }
            if(col) ans = true;

            boolean row = true;
            for(int j = 0; j < 3; j++)
            {
                row &= v[j][i];
            }
            if(row) ans = true;
        }

        if(v[0][0] && v[1][1] && v[2][2]) ans = true;
        if(v[0][2] && v[1][1] && v[2][0]) ans = true;
        if(ans) out.println("Yes");
        else out.println("No");
    }
    void a() throws Exception
    {
        int n = readInt();
        
        out.println((n + 1) / 2);
    }
}

Measured memory_bytes: 22740