random

/*
 Author: 曹北健(37509)
 Result: AC Submission_id: 4279424
 Created at: Wed Apr 06 2022 15:36:38 GMT+0800 (China Standard Time)
 Problem: 5486  Time: 365   Memory: 2720
*/

#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <string.h>
#include <ctype.h>
#include <time.h>
#pragma warning(disable:4996)
int main(){
#ifdef _DEBUG
    FILE *fp = freopen("../../../input.txt", "r", stdin);
    //FILE *fp2 = freopen("output.txt", "w", stdout);
#endif // _DEBUG
    srand(time(0));
    double x, y;
    double ub;
    int i, n = 0;
    scanf("%lf", &ub);
    //rand();//[0,32767]
    for(i = 0; i < 1919810; i++){
        x = (double)(rand() % RAND_MAX) / (double)RAND_MAX * ub;//[0,ub]
        y = (double)(rand() % RAND_MAX) / (double)RAND_MAX;
        if(exp(-pow(x + 0.5, 2)) > y){
            n++;
        }
    }
    printf("%.6f\n", exp(-((n / 1919810.) * ub)));

#ifdef _DEBUG
    freopen("CON", "r", stdin);
    //freopen("CON", "w", stdout);
    system("pause");
#endif // _DEBUG
    return 0;
}