#include <stdio.h>
#include <math.h>
#include <ctype.h>

#define REP(i,k,n) for(int i=k;i<n;i++)
#define rep(i,n) for(int i=0;i<n;i++)

typedef long long ll;


int main(void)
{
  int i,j,k,l;
  double a,b,x,y;
  double ans;
  scanf("%lf %lf %lf %lf",&a,&b,&x,&y);
  if( y/x >= b/a ) {
    ans = x;
    ans += (x * b) / a;
  }
  else {
    ans = y;
    ans += (y * a) / b;
  }
  printf("%lf\n",ans);
  return 0;
}