def extgcd(A,B):
    #return p,q such that Ap+Bq=1
    if A>B:
        q,p=extgcd(B,A)
        return p,q
    if A==0:
        if B==1:
            return 0,1
        else:
            return 0,0
    # B=cA+R then Ap+Bq=Ap+(cA+R)q=(cq+p)A+qR
    c=B/A
    R=B%A
    q,cqp=extgcd(R,A)
    return cqp-c*q,q

def gcd(A,B):
    if B<A:
        return gcd(B,A)
    if B%A==0:
        return A
    return gcd(B%A,A)

N=int(raw_input())
A,B=map(int,raw_input().split())
if A==0: 
    A=B
for i in range(N-1):
    X,Y=map(int,raw_input().split())
    if B>Y and B%Y==0 and A%B!=X%Y:
        print -1
        exit()
    elif B<Y and Y%B==0 and A%B!=X%Y:
        print -1
        exit()
    else:
        # find smallest A+Bp==X+Yq <=Bp-Yq=X-A
        g=gcd(B,Y)
        Y/=g
        #print "find ",A,"+",B,"p==",X,"+",Y,"q"
        p,q=extgcd(B,Y)
        #now Bp+Yq=1
        #print A,"+",B*Y,(p*(X-A))%Y 
        A=(p*(X-A)%Y)*B+A
        B*=Y
        if A<X:
            A=X
print A%1000000007