#include <bits/stdc++.h> using namespace std; int main(){ int a,b,c,d; cin>>a>>b>>c>>d; int max_ = max(a,b); max_ = max(max_,c); max_ = max(max_,d); int min_ = min(a,b); min_ = min(min_,c); min_ = min(min_,d); int count = (a+b+c+d) - max_ - min_; printf("%.2f",count / 2.0); return 0; }