#include #include #include #include #include #include #include #include #include #include #include #include using namespace std; int main() { int px, py, qx, qy; cin >> px >> py >> qx >> qy; double x = (double)abs(px - qx) / 2; double y = (double)abs(py - qy) / 2; cout << setprecision(20) << x+y << endl; return 0; }