#include <stdio.h>

int main() {
    int n = 0;
    scanf("%d", &n);

    int i = 0, flag = 1, tem = 1;
    float sum = 0.0f, result = 0.0f;
    for (i = 1; i <= n; i++) {
        sum += flag * tem;
        result += 1.0 / (sum);
        flag = -flag;
        tem += 2;
    }

    printf("%.3f", result);

    return 0;
}