#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include <math.h>

double random(double val1, double val2){
    return (double)rand() / RAND_MAX * (val2 - val1) + val1;
}

double value(double x){
    return x * x;
}

int increasing(double x, double y){
    if(y > 0 && y <= value(x)) return 1;
    if(y < 0 && y >= value(x)) return -1;
    return 0;
}

int main(void) {
    srand(time(NULL));
    int xp, xk, yp, yk;
    int n;
    scanf("%d%d%d%d%d", &xp, &xk, &yp, &yk, &n);
    double poleProstokata = abs(xk - xp) * abs(yk - yp);
    int c = 0;
    int licznik = n;
    while(licznik--){
        double x = random(xp, xk);
        double y = random(yp, yk);
        c += increasing(x, y);
    }
    double calka = poleProstokata * c / n;
    printf("%f", calka);
}