def pregarner(r,m):
    def gcd(a,b):
        if b==0:
            return a
        return gcd(b,a%b)
    n=len(m)

    for i in range(n):
        for j in range(i):
            g=gcd(m[i],m[j])
            if (r[i]-r[j])%g!=0:
                return False
            
            m[i]//=g;m[j]//=g
            gi=gcd(m[i],g)
            gj=g//gi

            while gcd(gi,gj)!=1:
                h=gcd(gi,gj)
                gi*=h
                gj//=h
            
            m[i]*=gi
            m[j]*=gj
    
    return True

def garner(r,m,MOD):
    def extgcd(a,b):
        if b==0:
            return 1,0,a
        else:
            c,x,g=extgcd(b,a%b)
            return x,c-a//b*x,g
    
    def modinv(a,m):
        x,_,_=extgcd(a,m)
        return x%m
    
    n=len(r)
    m.append(MOD)

    constants=[0]*(n+1)
    coeffs=[1]*(n+1)
    
    for k in range(len(r)):
        t=(r[k]-constants[k])*modinv(coeffs[k],m[k])%m[k]
        for i in range(k+1,len(m)):
            constants[i]=(constants[i]+t*coeffs[i])%m[i]
            coeffs[i]=coeffs[i]*m[k]%m[i]

    return constants[-1], coeffs[-1]

N=int(input())
X,Y=[],[]

for _ in range(N):
    x,y=map(int,input().split())
    X.append(x)
    Y.append(y)

if not pregarner(X,Y):
    print(-1)
else:
    res,l=garner(X,Y,10**9+7)
    if res==0:
        print(l)
    else:
        print(res)