#include <bits/stdc++.h>
using namespace std;
#define rep(i, n) for (int i = 0; i < (int)(n); ++i)
int main() {
    // Input
    int x, y, r;
    cin >> x >> y >> r;

    // All Search
    x = abs(x);
    y = abs(y);
    for (int a = 0; ; ++a) {
        if (x + y < a && 2 * r * r < abs(x + y - a) * abs(x + y - a)) {
            cout << a << endl;
            return 0;
        }
    }
}