random-integral

/*
 Author: 曹北健
 Result: AC Submission_id: 4269402
 Created at: Sat Apr 02 2022 19:34:52 GMT+0800 (China Standard Time)
 Problem_id: 5486   Time: 24    Memory: 2740
*/

#include <stdio.h>
#include <math.h>
double f(double t){
    return exp(-((t + 0.5) * (t + 0.5)));
}
double calcrnd(int testcnt, double lbx, double ubx, double lby, double uby){
    int cnt = 0, i;
    double x, y;
    for(i = 1; i <= testcnt; i++){
        x = ((rand() % 32768) / 32768.0) * (ubx - lbx) + lbx;
        y = ((rand() % 32768) / 32768.0) * (uby - lby) + lby;
        if(y < f(x))cnt++;
    }
    return (double)cnt / (double)testcnt * (ubx - lbx) * (uby - lby);
}
int main(){
    double ub;
    scanf("%lf", &ub);
    printf("%.6f\n", exp(-calcrnd(114514, 0, ub, 0, 1)));
    return 0;
}