N, M = map(int, input().split())
if M==0:
    keta = [['0']*N]
    if N!=1:
        keta[0]=1
    ans = ""
    for k in keta:
        ans = ans + k
    ans = int(ans)
    print(ans)
else:
    keta_list = [[-1]*(N) for i in range(M)]
    b_ans = True

    #initialization
    s, c = map(int, input().split())
    keta_list[0][s-1] = c

    for i in range(M-1):
        s_t, c_t = map(int, input().split())
        s_t = s_t - 1
        if keta_list[i][s_t] == -1:
            keta_list[i][s_t] = c_t
            for j in range(i,M-1):
                for k in range(N):
                    keta_list[j+1][k] = keta_list[j][k]
        elif keta_list[i][s_t]!=c_t:
            b_ans = False
            break
        else: # same num
            for j in range(i,M-1):
                for k in range(N):
                    keta_list[j+1][k] = keta_list[j][k]

    if b_ans:
        # list search
        ans_list = keta_list[M-1]
        for i in range(len(ans_list)):
            if ans_list[i]==-1:
                ans_list[i] = 0
        # sentou shori
        if ans_list[0]==0:
            print(-1)
        else:
            ans = ""
            for a in ans_list:
                ans = ans + str(a)
            ans = int(ans)
            print(ans)
    else:
        print(-1)


### FIXED CODE ###

N, M = map(int, input().split())
if N==1:
    if M==0:
        print(0)
    elif M==1:
        print(list(map(int,input().split()))[1])
    else:
        c = list(map(int, input().split()))[1]
        check=True
        for i in range(M):
            if list(map(int, input().split()))[1]!=c:
                check=False
                break
        if check:
            print(c)
        else:
            print(-1)
else:
    if M==0:
        keta = [0]*N
        keta[0] = 1
        ans = ""
        for i in range(N):
            ans = ans + str(keta[i])
        print(ans)
    elif M>=1:
        keta_list = [[-1]*(N) for i in range(M)]
        b_ans = True

        #initialization
        s, c = map(int, input().split())
        keta_list[0][s-1] = c

        for i in range(M-1):
            s_t, c_t = map(int, input().split())
            s_t = s_t - 1
            if keta_list[i][s_t] == -1:
                keta_list[i][s_t] = c_t
                for j in range(i,M-1):
                    for k in range(N):
                        keta_list[j+1][k] = keta_list[j][k]
            elif keta_list[i][s_t]!=c_t:
                b_ans = False
                break
            else: # same num
                for j in range(i,M-1):
                    for k in range(N):
                        keta_list[j+1][k] = keta_list[j][k]

        if b_ans:
            # list search
            ans_list = keta_list[M-1]
            for i in range(len(ans_list)):
                if ans_list[i]==-1 and i==0:
                    ans_list[i] = 1
                elif ans_list[i]==-1:
                    ans_list[i] = 0
            # sentou shori
            if ans_list[0]==0:
                print(-1)
            else:
                ans = ""
                for a in ans_list:
                    ans = ans + str(a)
                ans = int(ans)
                print(ans)
        else:
            print(-1)