#python
import math
def cdf(m, std, x):
    return 0.5 * (1 + math.erf((x-m)/(std*2**.5)))
n, m0, std0, x=100, 2.4, 2, 250
m=n*m0
std=math.sqrt(n)*std0
print(round(cdf(m, std, x), 4))

import math as m
def cdf(mn, std, x):
    return 1/2 * (1 + m.erf((x-mn)/(std*m.sqrt(2))))
print(f'{cdf(2.4*100, 2*m.sqrt(100), 250):.4f}')

double mean = 2.4;
double stdDev = 2.0;
int nStudents = 100;
int nTickets = 250;

double meanX = mean * nStudents;
double stdDevX = stdDev * Math.sqrt(nStudents);

double p = probability(meanX, stdDevX, nTickets);

  function erf(x) {
        var a1 = 0.254829592;
        var a2 = -0.284496736;
        var a3 = 1.421413741;
        var a4 = -1.453152027;
        var a5 = 1.061405429;
        var p = 0.3275911;
        var sign = 1;
        if (x < 0) {
            sign = -1;
        }
        x = Math.abs(x);
        var t = 1.0 / (1.0 + p * x);
        var y = 1.0 - (((((a5 * t + a4) * t) + a3) * t + a2) * t + a1) * t * Math.exp(-x * x);
        return sign * y;
    }
     let arr = input.split(/[\n]/g);
     let st = (parseFloat(arr[0]) - (parseInt(arr[1]) * parseFloat(arr[2]))) / (Math.sqrt(parseInt(arr[1])) * parseFloat(arr[3]));
     let ans = (1.0 + erf(st / Math.sqrt(2.0))) / 2.0;
    console.log(ans.toFixed(4));

from math import *
def Zscore(x):
    return (1.0 + erf(x / sqrt(2.0))) / 2.0

sumN = int(input())
n = int(input())
u = float(input())
o = float(input())

pr = (sumN - n*u) / (sqrt(n) * o)
x = Zscore(pr)
print(round(x, 4))