#include <cstdlib> #include <cmath> #include <climits> #include <cfloat> #include <map> #include <utility> #include <set> #include <iostream> #include <memory> #include <string> #include <vector> #include <algorithm> #include <functional> #include <sstream> #include <deque> #include <complex> #include <stack> #include <queue> #include <cstdio> #include <cctype> #include <cstring> #include <ctime> #include <iterator> #include <bitset> #include <numeric> #include <list> #include <iomanip> #include <cassert> #include <array> #include <tuple> #include <initializer_list> #include <unordered_set> #include <unordered_map> #include <forward_list> using namespace std; using ll = long long; #define rep(i,k) for (int i = 0; i < (int)(k); i++) #define all(cnt) begin(cnt), end(cnt) int main() { int a, b, c, d; while(cin >> a >> b >> c >> d) cout << fixed << setprecision(2) << (abs(a - c) + abs(b - d)) / 2. << endl; }