/*
TASK:minjumps
LANG:C++
*/
#include<iostream>
using namespace std;
int main()
{
int a,b,n;
cin>>a>>b>>n;
if(a>b)
{
a=b+a;
b=a-b;
a=a-b;
}
if(b-a==0)
{
if(n%b==0)
cout<<n/b<<"\n";
else if(n%a)
cout<<n/a<<"\n";
}
else if((n%b)%(b-a)==0)
cout<<n/b+2*((n%b)/(b-a))<<"\n";
else if((n%a)%(b-a)==0)
cout<<n/a+2*((n%a)/(b-a))<<"\n";
else if(n%(b-a)==0)
cout<<2*(n/(b-a))<<"\n";
else cout<<-1<<"\n";
return 0;//LopiTo
}
