/*  
   slope.c 
      find the slope of a line, to compile type
	gcc slope.c -lm -o cslope
*/

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

main()
{
    	int j;
        double m, b[4];

	for (j=0;j<=3;j=j+1)
                scanf("%lf",&b[j]);

	m = (b[3]-b[2]) / (b[1]-b[0]);

	printf("%lf\n",m);

}