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