/*
TASK:minjumps
LANG:C++
*/
#include <iostream>
using namespace std;
int a,b,c,n,br,brm=99999,k;
void rec(int p)
     {
//      cout<<p<<endl;
//      getchar();
      int f=0;      
      if(p==n){if(br<brm)brm=br;k=1;return;}
      if(k==1)return;
      if( (n-p) >=a){f=1;br+=f;rec(p+a);}
      if(f){br-=f;p-=a;}
      if( (n-p) >=b){f=1;br+=f;rec(p+b);}      
      if(f){br-=f;p-=b;}
      if( (n-p) >=c){f=2;br+=f;rec(p+c);}
      if(f){br-=f;p-=c;}      
      }
int main ()
{
int i,j;
scanf("%d%d%d",&a,&b,&n);
if(a%2==b%2&&a%2==0&&n%2==1){printf("-1\n");exit(0);}
c=abs(a-b);
rec(0);
int x;x=a;a=b;b=x;
k=0;
br=0;
//cout<<n<<"  "<<b<<"  "<<n%b<<endl;
rec(0);
cout<<brm<<endl;
}
