#include <bits/stdc++.h>
using namespace std;
int main() {
int a,b,c,d;
    cin>>a>>b>>c>>d;
    int sum = a+b+c+d;
    int x = max(max(a,b),max(c,d));
    int n = min(min(a,b),min(c,d));
    double s = (sum - x - n) / 2.0;
    cout << fixed << setprecision(2) << s;
    return 0;
}