#include <bits/stdc++.h>

//#pragma GCC optimize("unroll-loops")
//#pragma GCC optimize("Ofast")
//#pragma GCC target("sse,sse2,sse3,ssse3,sse4")
//#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")

#define F first
#define S second
#define pb push_back
#define ll long long
#define ld long double
#define endl '\n'
#define pii pair <int, int>
#define pll pair <ll, ll>
#define pld pair <ld, ld>

using namespace std;

const int N = 1e3 + 5;

int main() {
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
#ifdef LOCAL
    freopen("input.txt", "r", stdin);
    freopen("output.txt", "w", stdout);
#else
    freopen("garden.in", "r", stdin);
    freopen("garden.out", "w", stdout);
#endif
    int x, y;
    cin >> x >> y;
    x = abs(x);
    y = abs(y);
    if (!((x % 2 && y % 2) || (x % 4 == 0 && y % 4 == 0))) {
        cout << -1;
        return 0;
    }
    int k1 = x / 4;
    int k2 = y / 4;
    ld ans = 0;
    ans += (2 * sqrt(2) + 4) * min(k1, k2);
    x -= min(k1, k2) * 4;
    y -= min(k1, k2) * 4;
    if (x < y) {
        swap(x, y);
    }
    if (y == 3) ans += 2;
    ans += (x / 4) * (2 + 2 * sqrt(2));
    x %= 4;
    if (x == 1) ans += sqrt(2);
    if (x == 3) ans += sqrt(2) + 2;
    cout << fixed << setprecision(10) << ans;
    return 0;
}