1005：地球人口承载力估计

#include <iostream>
#include <cstdio>
using namespace std;
int main()
{
    int x,a,y,b;
    cin>>x>>a>>y>>b;
    printf("%.2lf\n",1.0*( ( x*a-y*b ) / (a-b) ) );
    return 0;
}