Contest1184/A.java

public class A {
    public static void main(String[] args) {
        double s = 0;
        for (int i = 1; i <= 100; i++) {
            if (i % 2 == 1)
                s += 1.0 / i;
            else
                s -= 1.0 / i;
        }
        System.out.println(String.format("%.8f", s));

    }
}