N,M=map(int,input().split())
s=[0]*M
c=[0]*M
for i in range(M):
    s[i],c[i]=map(int,input().split())

if M==0:
    print(-1)
else:
    
    if N==1:
        flag_1=0
        for i in range(M-1):
            for j in range(i+1,M):
                if c[i]!=c[j]:
                    flag_1+=1
        if flag_1==0:
            print(c[0])
        else:
            print(-1)

    elif N==2:
        flag_2_ok=0
        for i in range(M):
            if s[i]==1 and c[i]!=0:
                flag_2_ok+=1
        if flag_2_ok>=1:
            ans_2=10
            flag_2=0
            flag_2_ten=0
            flag_2_one=0
            for i in range(M-1):
                for j in range(i+1,M):
                    if s[i]==s[j]:
                        if c[i]!=c[j]:
                            flag_2+=1
            if flag_2==0:
                for i in range(M):
                    if s[i]==1 and flag_2_ten==0:
                        ans_2+=10*c[i]-10
                        flag_2_ten+=1
                    if s[i]==2 and flag_2_one==0:
                        ans_2+=c[i]
                        flag_2_one+=1
                print(ans_2)
            else:
                print(-1)
        else:
            print(-1)
        
    elif N==3:
        flag_3_ok=0
        for i in range(M):
            if s[i]==1 and c[i]!=0:
                flag_3_ok+=1
        if flag_3_ok>=1:
            ans_3=100
            flag_3=0
            flag_3_hun=0
            flag_3_ten=0
            flag_3_one=0
            for i in range(M-1):
                for j in range(i+1,M):
                    if s[i]==s[j]:
                        if c[i]!=c[j]:
                            flag_3+=1
            if flag_3==0:
                for i in range(M):
                    if s[i]==1 and flag_3_hun==0:
                        ans_3+=100*c[i]-100
                        flag_3_hun+=1
                    if s[i]==2 and flag_3_ten==0:
                        ans_3+=10*c[i]-10
                        flag_3_ten+=1
                    if s[i]==3 and flag_3_one==0:
                        ans_3+=c[i]
                        flag_3_one+=1
            print(ans_3)
        else:
            print(-1)
    else:
        print(-1)