/*
task:minjumps
lang:c++
*/
#include<iostream>
using namespace std;
int a,b,n, br=0, min1=0;
int search(int i)
{
    if(i==n){cout<<br<<endl; min1=1; }
    if(i>n) {br--;return 1;}
    if(min1!=0) return 1;
    else
    {
	br++;
	search(i+a);
	search(i+b);
	br++;
	search(i-b);
    br++;
	search(i-a);

	br=br-1;
    }
    return 1;
}
int main()
{
    cin>>a>>b>>n;
    int p=0;
    if(a%2==0&&b%2==0&n%2==1)
    cout<<-1<<endl;
       else {search(p);
    }
    return 0;
}
