import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.rmi.dgc.Lease;
import java.util.Arrays;
import java.util.NoSuchElementException;

public class Main {
    public static void main(String[] args) {
        Main main = new Main();
        main.solve();
        main.out.close();
    }
    // ======================================================================
    public void solve() {
    	int N = ni();
    	int M = ni();
    	int s, c;
    	char[] CC = new char[N];
    	Arrays.fill(CC, 'X');
    	boolean f = true;
    	for (int i = 0; i <M; i++) {
			s = ni();
			c = ni();
			if(CC[s-1] != 'X' && CC[s-1] != (char)('0'+c)) {
				f = false;
			}
			CC[s - 1] = (char)('0'+c);
		}
    	if(!f) {
			out.println(-1);
			return;
    	}
    	for (int i = 0; i < N; i++) {
			if(CC[i] == 'X') {
				if(i == 0 && N != 1)		CC[i] = '1';
				else			CC[i] = '0';
			}
		}
    	Integer ans = Integer.valueOf(String.valueOf(CC));
    	if(ans.toString().length() != N)	out.println(-1);
    	else								out.println(ans);
    }
    // ------------------------------------------
    // ライブラリ
    // ------------------------------------------
    // Print
	private PrintWriter out = new PrintWriter(System.out);

    // Scanner
    private FastScanner scan = new FastScanner();
    int ni(){ return scan.nextInt();}
    int[] ni(int n){int[] a = new int[n]; for(int i = 0; i < n; i++){a[i] = ni();} return a;}
    int[][] ni(int y, int x){int[][] a = new int[y][x];
        for(int i = 0; i < y; i++){for(int j = 0; j < x; j++){a[i][j] = ni();}} return a;}
    long nl(){return scan.nextLong();}
    long[] nl(int n){long[] a = new long[n]; for(int i = 0; i < n; i++){a[i] = nl();} return a;}
    long[][] nl(int y, int x){long[][] a = new long[y][x];
        for(int i = 0; i < y; i++){for(int j = 0; j < x; j++){a[i][j] = nl();}} return a;}
    String ns(){return scan.next();}
    String[] ns(int n){String[] a = new String[n]; for(int i = 0; i < n; i++){a[i] = ns();} return a;}
    String[][] ns(int y, int x){String[][] a = new String[y][x];
        for(int i = 0; i < y; i++){for(int j = 0; j < x; j++){a[i][j] = ns();}} return a;}
}
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: 23124