/*
TASK: minjumps
LANG: C++
*/
#include<iostream>
#include<cstdio>
using namespace std;
int main()
{
    int n,a,b,i=0,j,br=0,tmp;
    cin>>a>>b>>n;
    if(n<0)n=n*-1;
    if(a<b)
    {
           tmp=a;
           a=b;
           b=tmp;
    }
    if(n>100)
    {
             cout<<"-1"<<"\n";
             return 0;
    }
    br+=n/a;
    i=br*a;
    tmp=(n-i)/b;
    i+=tmp*b;
    br+=tmp;
    if(i!=n)
    {
            n=n-i;
            tmp=a-b;
            
            if(n%tmp==0)
            {
                       br+=(n/tmp)*2;
                       cout<<br<<"\n";
                       return 0;
            }
            br+=2;
            while(n!=tmp)
            {
             
                         tmp=tmp-b;
                         if(tmp<0)
                         {
                                  cout<<-1<<"\n";
                                  return 0;
                         }
                         br+=1;
             }
    }

    cout<<br<<"\n";
   
    return 0;
}
                
