NUMORDERED

#include <iostream>
#include <cmath>

using namespace std;

bool check(unsigned long long& d,long long& m,long long& n){
    long long k = min((long long)sqrt((long double)d/2.0),m), j;
    for(int i =1; i<=k; i++){
        j = (long long)sqrt((long double)(d-i*i));
        if(j*j == d - i*i && j<=n) return true;
    }
    return false;
}

inline long long timk(unsigned long long& d,long long& m,long long& k,long long& n){
    long long dem = 0,j;
    for(int i=1; i<=m; i++){
        j = d - i*i;
        if(j >= 0)
            dem += min((long long)sqrt((long double) j ),n);
        else break;
    }
    return dem;
}

int main(){
    long long m,n,k;
    cin >> m >> n >> k;
    if(m>n) swap(m,n);
    unsigned long long L = 2,H = m*m + n*n , d;
    d = (L+H+1)/2 ;
    long long p = timk(d,m,k,n);

    while(k != p || !check(d,m,n)){
        if(k != p){
            L = (k>p ? d+1 : L);
            H = (k>p ? H : d-1);
            if(d == (L+H+1)/2) break;
            d = (L+H+1)/2;
            p = timk(d,m,k,n);
            //cout << d;
        }
        else d--;
    }
    cout << d;
}