#!/usr/bin/env python3
import sys


def solve(N: int, M: int, s: "List[int]", c: "List[int]"):
    sc=[]
    for i in range(M):
        sc.append([s[i],c[i]])
    sc=list(map(list,set(map(tuple,sc))))
    sc.sort()
    for i in range(len(sc)):
        if sc[i][0]==1 and sc[i][1]==0:
            print(-1)
            exit()
    if M==0 and N==1:
        print(0)
        exit()
    if M==0 or len(sc)==1 and c[0]==0 and not s[0]==1:
        q=[1]
        for i in range(N-1):
            q.append(0)
        print("".join(map(str,q)))
        exit()
    for i in range(len(sc)-1):
        if sc[i][0]==sc[i+1][0]:
            print(-1)
            exit()
    #if N>max(set(s)):
    #    print(-1)
    #    exit()
    a=[0]*N
    for i in range(len(s)):
        a[s[i]-1]=c[i]
    if a[0]==0:
        a[0]=1
    print("".join(map(str,a)))
    return


# Generated by 1.1.6 https://github.com/kyuridenamida/atcoder-tools  (tips: You use the default template now. You can remove this line by using your custom template)
def main():
    def iterate_tokens():
        for line in sys.stdin:
            for word in line.split():
                yield word
    tokens = iterate_tokens()
    N = int(next(tokens))  # type: int
    M = int(next(tokens))  # type: int
    s = [int()] * (M)  # type: "List[int]"
    c = [int()] * (M)  # type: "List[int]"
    for i in range(M):
        s[i] = int(next(tokens))
        c[i] = int(next(tokens))
    solve(N, M, s, c)

if __name__ == '__main__':
    main()
