simpson

/*
 Author: 曹北健
 Result: AC Submission_id: 4279111
 Created at: Wed Apr 06 2022 07:37:06 GMT+0800 (China Standard Time)
 Problem_id: 5486   Time: 14    Memory: 2672
*/

#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <string.h>
#include <ctype.h>
#pragma warning(disable:4996)
typedef long long LL;
typedef unsigned long long ULL;
double lam(double t){
    return exp(-((t + 0.5) * (t + 0.5)));
}
double simpson(int ndiv, double lb, double ub, double(*pfunc)(double)){
    double h = (ub - lb) / ndiv;
    double s = pfunc(lb) + pfunc(ub);
    int i;
    for(i = 1; i < ndiv; i += 2){
        s += 4 * pfunc(lb + i * h);
    }
    for(i = 2; i < ndiv - 1; i += 2){
        s += 2 * pfunc(lb + i * h);
    }
    return s * h / 3.;
}
int main(){
    double ub;
    scanf("%lf", &ub);
    printf("%.6f\n", exp(-simpson(114514, 0, ub, lam)));
    return 0;
}