/*
TASK: minjumps
LANG: C++
*/
#include<iostream.h>
#include<math.h>
long a,b,n,min,max,sum,br;
int main()
{  cin>>a>>b>>n;
  if(a>b) { max=a; min=b; }
  else { max=b; min=a; }
  if(a%2==0 && b%2==0 && n%2==1) sum=-1;
  else if(n%max==0) sum=n/max;
  else if(n%min==0) sum=n/min;
   else sum=b*a;
  cout<<sum<<endl;
 return 0;
}
