#define _USE_MATH_DEFINES #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include using namespace std; typedef long double ld; typedef long long ll; typedef unsigned long long ull; typedef pair i_i; typedef pair ll_i; typedef pair i_ll; typedef pair d_i; typedef pair ll_ll; typedef pair d_d; struct edge { int u, v; ll w; }; ll MOD = 10007; ll _MOD = 1000000009; double EPS = 1e-10; int main() { int a, b, c, d; cin >> a >> b >> c >> d; cout << (abs(a - c) + abs(b - d)) / 2.0 << endl; }