#include
int main() {
double e, i, j, k, s;
i = 1.0;
j = 1.0;
k = 1.0;
printf("Input e:");
scanf("%lf", &e);
if (e < 0) e = -e;
s = 0.0;
while((i - e) > 0) {
s = s + i * k;
j += 4.0;
i = 1.0 / j;
k *= -1.0;
}
printf("S = %8.6lf\n", s);
}