#include <iostream>
#include <algorithm>
#include <cstdio>
#include <vector>
#include <cstring>
#include <string>
#include <cmath>
#include <utility>
#include <map>
#include <set>
#include <queue>
#include <stack>
#include <sstream>
#define fr(a,b,c) for (int a=b;a<=c;a++)
#define frr(a,b,c) for (int a=b;a>=c;a--)
#define rep(a,b) for (int a=0;a<b;a++)
#define repp(a,b) for (int a=b-1;a>=0;a--)
#define pb push_back
#define mp make_pair
#define fi first
#define se second
#define sz(a) int(a.size())
#define all(a) a.begin(),a.end()
#define reset(a,b) memset(a,b,sizeof(a))
#define pii pair<int,int>
#define oo 1LL<<60
#define maxN 1
using namespace std;

struct RectangularSum
{
    long long att(int h,int w,long long S,int H,int W)
    {
        long long u = S*4/h/w - 2LL*W*(h-1) + 2 - 2*w;
        if (u%4 || u<0) return oo;
        u/=4;
        return u/W + h <= H && u%W + w <= W ? 1LL*w*h : oo;
    }

    long long minimalArea(int height, int width, long long S)
    {
        long long ans=oo;

        vector <int> listW;
        for (int i=1;i<=width;i++)
            if (S*4%i==0) listW.push_back(i);

        fr(h,1,height)
            if (S*4%h==0)
                for (int i=0;i<listW.size();i++)
                    if (S*4/h%listW[i]==0)
                        ans=min(ans,att(h,listW[i],S,height,width));

        return ans==oo?-1:ans;
    }
};