import java.io.*;
import java.util.*;
class Main{
	static final long MOD = 1_000_000_007; // 10^9+7
    static final int MAX = 2_147_483_646; // intMax 
    static final int INF = 1_000_000_000; // 10^9  
    public static void main(String[] args) throws Exception {
		hayami saori = new hayami();
		int n = saori.saori_hayami();
		int m = saori.saori_hayami();
		int[] ans = new int[n+1];
		boolean[] view = new boolean[n+1];
		int s = 0;
		int c = 0;
		boolean flg = true;
		for(int i = 1;i <= m;i++){
			s = saori.saori_hayami();
			c = saori.saori_hayami();
			if(view[s] == false){
				ans[s] = c;
				view[s] = true;
			} else {
				if(ans[s] == c){

				} else{
					flg = false;
				}
			}
		}
		int ansflg = 1;
		if(flg){
			for(int i = 1;i <= n;i++){
				if(view[i]){
					if(ans[1] == 0 && n != 1){
						ansflg = -1;
					} else if(ans[1] == 0 && n == 1){
						ansflg = 0;
					}
				} else {
					if(i == 1){
						ans[i] = 1;
					} else {
						ans[i] = 0;
					}
				}
			}
		} else {
			ansflg = -1;
		}
		if(ansflg == 1){
			for(int i = 1;i <= n;i++){
				System.out.print(ans[i]);
			}
			System.out.println("");
		} else if(ansflg == 0){
			System.out.println(0);
		} else if(ansflg == -1){
			System.out.println(-1);
		}
		
		saori.close();
    }
}

class hayami implements Closeable {
	private final InputStream in = System.in;
	private final byte[] hayami = new byte[1024];
	private int Hayami = 0;
	private int saori = 0;
	private boolean HayamiSaori() {
		if (Hayami < saori) {
			return true;
		}else{
			Hayami = 0;
			try {
				saori = in.read(hayami);
			} catch (IOException e) {
				e.printStackTrace();
			}
			if (saori <= 0) {
				return false;
			}
		}
		return true;
	}
	private int SaoriHayami() { 
		if (HayamiSaori()) {
            return hayami[Hayami++];
         }else{
             return -1;
         }
	}
	private static boolean hayami_saori(int hayami) { 
		return 33 <= hayami && hayami <= 126;
	}
	public boolean hayamisaori() { 
		while(HayamiSaori() && !hayami_saori(hayami[Hayami])) Hayami++; return HayamiSaori();
	}
	public String nextHayami() {
		if (!hayamisaori()) throw new NoSuchElementException();
		StringBuilder hayamin = new StringBuilder();
		int saori = SaoriHayami();
		while(hayami_saori(saori)) {
			hayamin.appendCodePoint(saori);
			saori = SaoriHayami();
		}
		return hayamin.toString();
	}
	public long saorihayami() {//nextLong
		if (!hayamisaori()) throw new NoSuchElementException();
		long hayami = 0;
		boolean misao = false;
		int saori = SaoriHayami();
		if (saori == '-') {
			misao = true;
			saori = SaoriHayami();
		}
		if (saori < '0' || '9' < saori) {
			throw new NumberFormatException();
		}
		while(true){
			if ('0' <= saori && saori <= '9') {
				hayami *= 10;
				hayami += saori - '0';
			}else if(saori == -1 || !hayami_saori(saori)){
				return misao ? -hayami : hayami;
			}else{
				throw new NumberFormatException();
			}
			saori = SaoriHayami();
		}
	}
	public int saori_hayami() {//nextInt
		long hayami = saorihayami();
		if (hayami < Integer.MIN_VALUE || hayami > Integer.MAX_VALUE) throw new NumberFormatException();
		return (int) hayami;
	}
	public double Hayamin() { //nextDouble
		return Double.parseDouble(nextHayami());
	}
	public void close() {
		try {
			in.close();
		} catch (IOException e) {
		}
    }
    
}