#include <iostream>
#include<math.h>
using namespace std;

int maxval(int a, int b, int c){
    int tmp=a;
    if(tmp<b)tmp=b;
    if(tmp<c)tmp=c;
    return tmp;
}

int main() {
    int P,T,G1,G2,G3,GJ;
    while (cin >> P>>T>>G1>>G2>>G3>>GJ) { // 注意 while 处理多个 case
        if(abs(G1-G2)<=T)printf("%.1f\n",(G1+G2)*1.0/2);
        else {
            if(abs(G3-G1)<=T&&abs(G3-G2)>T){
                printf("%.1f\n",(G3+G1)*1.0/2);
            }
            else if(abs(G3-G2)<=T&&abs(G3-G1)>T){
                printf("%.1f\n",(G3+G2)*1.0/2);
            }
            else if(abs(G3-G1)<=T&&abs(G3-G2)<=T){
                printf("%.1f\n",1.0*maxval(G1,G2,G3));
            }
            else {
                printf("%.1f\n",1.0*GJ);
            }
        }
    }
}
// 64 位输出请用 printf("%lld")