#include <iostream>
using namespace std;
int main() {
int x, y , k;
cin>>x>>y>>k;
int s=abs(x)+abs(y), ost=0, t=0;
if(x==0 && y==0) ost=1;
else if (x==0 || y==0) ost=2;
if(x*y==0) t=1;
if(k==1 && x*y==0 || k==2 && x*y!=0) cout<<s;
else if(k%4==ost){
cout<<s+k/4+t;
} else {
cout<<-1;
}
return 0;
}
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