/*
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INPUT:                            |
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OUTPUT:                           |
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*/

#include<bits/stdc++.h>
using namespace std;

#define ll long long
#define el "\n"

ll n, m, k, l, r, ans;

ll f(ll x)
{
    ll c = 0;
    for (ll i = 1; i <= m; i++)
    {
        if (x - i * i < 0)
        {
            break;
        }
        ll j = sqrt(x - i * i);
        while ((j + 1) * (j + 1) <= x - i * i)
        {
            j++;
        }
        while (j * j > x - i * i)
        {
            j--;
        }
        c += min(n, j);
    }
    return c;
}

int main()
{
    ios_base::sync_with_stdio(0);
    cin.tie(0);cout.tie(0);
    
//    freopen("BAI1.INP" , "r" , stdin);
//    freopen("BAI1.OUT" , "w" , stdout);
    
    cin >> n >> m >> k;
    if (m > n)
    {
        swap(m, n);
    }
    l = 2;
    r = m * m + n * n;
    while (l <= r)
    {
        ll mid = (l + r) / 2;
        if (f(mid) >= k)
        {
            ans = mid;
            r = mid - 1;
        }
        else
        {
            l = mid + 1;
        }
    }
    cout << ans;
}
/// Minh Khôi, Amsterdam school, the 10 math 1 class
/// user: Minhkhoitht