#include <stdio.h>

double funkcija(int n) {
    double result = 0.5;
    int brojac = 1;
    for(int i = 3; i <= n; i += 2) {
        if(brojac % 2 == 0) {
            result /= ( (double)i / (double)(i + 1) );
        }
        else {
            result *= ( (double)i / (double)(i + 1) );
        }
        brojac++;
    }
    return result;
}
int main (int argc, const char * argv[]) {
    int n;
    scanf("%d", &n);


    printf("%lf\n", funkcija(n));

    return 0;
}