N,M = map(int,input().split())

NN = ['A']*N
mujun = 0

for m in range(M):
    si,ci = map(int,input().split())
    if NN[si-1] == 'A':
        NN[si-1] = ci
    else:
        if NN[si-1] == ci:
            pass
        else:
            mujun = 1
            break
AA = []
for n in range(N):
    if n == 0:
        if NN[n] == 'A':
            AA.append('1')
        else:
            AA.append(str(NN[n]))
    else:
        if NN[n] == 'A':
            AA.append('0')
        else:
            AA.append(str(NN[n]))

if AA[0] == '0':
    mujun = 1
    
if mujun == 1:
    print('-1')
else:
    print(''.join(AA))