/*
TASK:CROSSING
LANG:C
*/
#include <stdio.h>
float w,s,a,b,time=0;
int main()
{   
    float to_kanue;
    scanf("%f%f%f%f",&w,&s,&a,&b);
    to_kanue=(w/2)*(w/2)/2;
    time+=2*(to_kanue/a);
    time+=(s-2*w)/b;
    printf("%f",time);
return 0;
}
    
