#include <bits/stdc++.h>
#define all(x) (x).begin(),(x).end()

using namespace std;
using ll = long long;

struct pt {
    int x;
    int y;
    int ind;
    pt(int cx = 0, int cy = 0, int cind = 0) {
        this->x = cx;
        this->y = cy;
        this->ind = cind;
    }
    bool operator < (const pt& o) {
        return x < o.x || (x == o.x && y < o.y);
    }
    pt operator - (const pt& o) const {
        return pt(x - o.x, y - o.y);
    }
};

int main() {
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
    cout.tie(nullptr);
    int ad, ac, bd, bc;
    cin >> ad >> ac >> bd >> bc;
    if (ad == bd && ac == bc) {
        cout << "Impossible." << endl;
        return 0;
    }
    auto get = [&] (double cosangle, int a, int b) {
        return sqrt(a * a + b * b - 2 * cosangle * a * b);
    };
    double k = ad * 1.0 / bc;
    double L1 = bd;
    double L2 = ac;
    /*
     *  (L1 - x) / y == (L2 - y) / x == AD / BC
     *  L1 - x = ky
     *  L2 - y = kx
     *  x = L1 - ky
     *  L2 - y = k (L1 - ky)
     *  L2 - y = kL1 - k**2 * y
     *  (k**2 - 1) y = kL1 - L2
     *  y = (kL1 - L2) / (k**2 - 1)
     *  x = L1 - ky
     */
    if (abs(k * k - 1) < 1e-10) {
        cout << "Impossible.\n";
        return 0;
    }
    double y = (k * L1 - L2) / (k * k - 1);
    double x = L1 - k * y;

    double cosA = (x * x + bc * bc - y * y) / (2 * bc * x);

    cout << fixed << setprecision(0) << "Distance is " << get(cosA, ac, ad) * 1000  << " km." << endl;
}