#include <stdio.h>

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

    double numerator = 2.0,    //和分母
            denominator = 1.0; //分子
    
    double oldNumerator = 0.0;

    double result = 0.0;
    for (int i = 0; i < n; ++i) {
        result += numerator / denominator;
        oldNumerator = numerator;
        numerator += denominator;
        denominator = oldNumerator;
    }

    printf("%.6f", result);
}