#include #include #include #include #include #include #include #include #include #include #include #include #include #include using namespace std; #define FOR(I,A,B) for(int I = (A); I < (B); ++I) typedef long long ll; int main(){ double x1, y1, x2, y2; cin >> x1 >> y1 >> x2 >> y2; double dy = fabs(y1 - y2); double dx = fabs(x1 - x2); double ans = (dy + dx) / 2.0; printf("%lf\n", ans); return 0; }