N,M = map(int,input().split())
 
m = []
for i in range(M):
    m.append(list(map(int,input().split())))
for i in range(10**N):
    a = str(i)
    
    if i >= 10**(N-1):
            
        for j in range(M):
            try:
                
                if a[m[j][0]-1] == str(m[j][1]):
                    True
                
                else:
                    break
            except:
                break
                
            if j == M-1:
                print(i)
                exit()
                
if M==0:
    if N == 1:
        print(0)
    else:
        print(10**(N-1))

elif M==1:
    if N == 1:
        m == [[1,0]]
        print(0)

else :
    print(-1)