/*
TASK:minjumps
LANG:C++
*/
#include <iostream.h>

double a,b,n,m=-1,x[201];

void jump(int p,int br)
{
   if(p==n)
            {
                    if(br<m||m==-1)
                    m=br;
                    }
     if((x[p+101]>br||x[p+101]==0)&&p!=n)
     {
            x[p+101]=br;
            if(p+a<=100) jump(p+a,br+1);
            if(p-a>=-100) jump(p-a,br+1);
            if(p+b<=100) jump(p+b,br+1);
            if(p-b>=-100) jump(p-b,br+1);
                        }
 }
int main()
{
    cin>>a>>b>>n;
    jump(0,0);
    cout<<m<<"\n";
    return 0;
}
