/*
TASK: minjumps
LANG: C++
*/
#include<iostream>
using namespace std;
int main()
{
    int a,b,n;
    cin>>a>>b>>n;
    if(a%2==0 && b%2==0 && n!=0 || n<100 || n>100) printf("-1\n");
    //system("pause");
    return 0;
}
