#include <stdio.h>
  main() {
	double i,j,s1,s2,s;
	s1 = 0;
	s2 = 0;
	for ( i = 1; i<=19; i+=2) {
		s1 += 1/i;
}	for ( j = 2; j<=20; j+=2) {
		s2 -= 1/j;
}	s = s1 + s2;
	printf("s= %f\n", s);
	return 0;
}