import java.util.*;
import java.io.*;

public class Main {
    public static void main(String[] args) {
        FastScanner fs = new FastScanner();
        int n = fs.nextInt();
        int m = fs.nextInt();
        int[] s = new int[m];
        int[] c = new int[m];
        for (int i=0;i<m;i++){
            s[i] = fs.nextInt();
            c[i] = fs.nextInt();
        }
        int start = 1,end;
        if(n==1){
            start = 0;
            end = 9;
        }else{
            for(int i=0;i<n-1;i++){
                start*=10;
            }
            end = start*10-1;
        }
        int i;

        for(;start<=end;start++){

            for(i=0;i<m;i++){
                int tmp = start;
                for(int j=0;j<n-s[i];j++){
                    tmp/=10;
                }
                if(tmp%10!=c[i]){
                    break;
                }
            }
            if(i==m){
                System.out.println(start);
                return;
            }
        }
        System.out.println(-1);


    }
    static class FastScanner {
            private final InputStream in = System.in;
            private final byte[] buffer = new byte[1024];
            private int ptr = 0;
            private int buflen = 0;
            private boolean hasNextByte() {
                if (ptr < buflen) {
                    return true;
                }else{
                    ptr = 0;
                    try {
                        buflen = in.read(buffer);
                    } catch (IOException e) {
                        e.printStackTrace();
                    }
                    if (buflen <= 0) {
                        return false;
                    }
                }
                return true;
            }
            private int readByte() { if (hasNextByte()) return buffer[ptr++]; else return -1;}
            private static boolean isPrintableChar(int c) { return 33 <= c && c <= 126;}
            public boolean hasNext() { while(hasNextByte() && !isPrintableChar(buffer[ptr])) ptr++; return hasNextByte();}
            public String next() {
                if (!hasNext()) throw new NoSuchElementException();
                StringBuilder sb = new StringBuilder();
                int b = readByte();
                while(isPrintableChar(b)) {
                    sb.appendCodePoint(b);
                    b = readByte();
                }
                return sb.toString();
            }
            public long nextLong() {
                if (!hasNext()) throw new NoSuchElementException();
                long n = 0;
                boolean minus = false;
                int b = readByte();
                if (b == '-') {
                    minus = true;
                    b = readByte();
                }
                if (b < '0' || '9' < b) {
                    throw new NumberFormatException();
                }
                while(true){
                    if ('0' <= b && b <= '9') {
                        n *= 10;
                        n += b - '0';
                    }else if(b == -1 || !isPrintableChar(b)){
                        return minus ? -n : n;
                    }else{
                        throw new NumberFormatException();
                    }
                    b = readByte();
                }
            }
            public int nextInt() {
                long nl = nextLong();
                if (nl < Integer.MIN_VALUE || nl > Integer.MAX_VALUE) throw new NumberFormatException();
                return (int) nl;
            }
            public double nextDouble() { return Double.parseDouble(next());}
        }
}

Measured memory_bytes: 32536