use std::io::*;
use std::str::FromStr;
/*
//use std::num;
//use std::cmp;
//use std::collections::VecDeque;
//use std::io::{self, BufRead};
const LOW_CASE_ALPHABET: [char; 26] = [
	'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's',
	't', 'u', 'v', 'w', 'x', 'y', 'z',
];
*/

fn main() {
	let mut a: isize = read();
	let mut b: isize = read();
	let c: usize = read();
	let d: isize = read();
	let e: isize = read();
	let mut ans: Vec<isize> = vec![0; c + 1];
	let mut tmp = 0;

	for _i in 0..=c{
		ans[_i] = a - b;

		a += d;
		b += e;
	}

	tmp = ans[0];

	for _i in 1..ans.len(){
		if ans[_i - 1] < ans[_i]{
			tmp = ans[_i];
		}
	}

	print!("{}",tmp);
}

/*
let mut temp = String::new();
	std::io::stdin().read_line(&mut temp).ok();
	let temp = temp
		.trim()
		.chars()
		.map(|c| c as usize - '0' as usize)
		.collect::<Vec<_>>();

	let mut iter = temp.iter(); // イテレータを取得

	let a: isize = *iter.next().unwrap() as isize;
	let b: isize = *iter.next().unwrap() as isize;
	let c: isize = *iter.next().unwrap() as isize;

*/
pub fn quicksort(numbers: &mut Vec<u64>) {
	if numbers.len() <= 1 {
		return;
	}

	let pivot = numbers.pop().unwrap();
	let mut lesser = Vec::new();
	let mut greater = Vec::new();

	for num in numbers.iter() {
		if *num <= pivot {
			lesser.push(*num);
		} else {
			greater.push(*num);
		}
	}

	quicksort(&mut lesser);
	quicksort(&mut greater);

	numbers.clear();
	numbers.extend(lesser);
	numbers.push(pivot);
	numbers.extend(greater);
}

pub fn is_leap_year(year: isize) -> bool {
	if ((year % 4 == 0) && (year % 100 != 0)) || (year % 400 == 0) {
		return true;
	} else {
		return false;
	}
}

pub fn ctoi(c: char) -> isize {
	let n = c as isize - '0' as isize;

	return n;
}

pub fn stoi(c: String) -> isize {
	let n = c.parse::<isize>().unwrap();

	return n;
}

pub fn find_char(sentence: Vec<char>, target: char, start: isize) -> isize {
	for _i in start as usize..sentence.len() {
		if sentence[_i] == target {
			return _i as isize;
		}
	}
	return -1;
}

pub fn hex_to_binary(hex_string: &str, x: u32) -> Option<String> {
	match i64::from_str_radix(hex_string, x) {
		Ok(decimal) => Some(format!("{}", decimal)),
		Err(_) => None,
	}
}

pub fn my_floor(x: f64) -> f64 {
	let rounded = (x * 1000.0).floor() / 1000.0;

	rounded
}

pub fn upper_lower(x: char) -> char {
	let result: char;

	if x.is_uppercase() {
		result = x.to_ascii_lowercase();
	} else if x.is_lowercase() {
		result = x.to_ascii_uppercase();
	} else {
		result = x;
	}

	result
}

pub fn maxf_2(x: f64, y: f64) -> f64 {
	let result;

	if x >= y {
		result = x;
	} else {
		result = y;
	}

	result
}

pub fn max_2(x: isize, y: isize) -> isize {
	let result;

	if x >= y {
		result = x;
	} else {
		result = y;
	}

	result
}

pub fn max_u_2(x: usize, y: usize) -> usize {
	let result;

	if x >= y {
		result = x;
	} else {
		result = y;
	}

	result
}

pub fn min_u_2(x: usize, y: usize) -> usize {
	let result;

	if x <= y {
		result = x;
	} else {
		result = y;
	}

	result
}

pub fn min_2(x: isize, y: isize) -> isize {
	let result;

	if x >= y {
		result = y;
	} else {
		result = x;
	}

	result
}

pub fn min_2_i32(x: i32, y: i32) -> i32 {
	let result;

	if x >= y {
		result = y;
	} else {
		result = x;
	}

	result
}

pub fn max_3(x: isize, y: isize, z: isize) -> isize {
	let result;
	if x >= y && y >= z {
		result = x;
	} else if x >= z && z >= y {
		result = x;
	} else if y >= x && x >= z {
		result = y;
	} else if y >= z && z >= x {
		result = y;
	} else if z >= x && x >= y {
		result = z;
	} else {
		result = z;
	}

	result
}

pub fn max_u_3(x: usize, y: usize, z: usize) -> usize {
	let result;
	if x >= y && y >= z {
		result = x;
	} else if x >= z && z >= y {
		result = x;
	} else if y >= x && x >= z {
		result = y;
	} else if y >= z && z >= x {
		result = y;
	} else if z >= x && x >= y {
		result = z;
	} else {
		result = z;
	}

	result
}

pub fn min_3(x: isize, y: isize, z: isize) -> isize {
	let result;
	if x <= y && y <= z {
		result = x;
	} else if x <= z && z <= y {
		result = x;
	} else if y <= x && x <= z {
		result = y;
	} else if y <= z && z <= x {
		result = y;
	} else if z <= x && x <= y {
		result = z;
	} else {
		result = z;
	}

	result
}

pub fn min_u_3(x: usize, y: usize, z: usize) -> usize {
	let result;
	if x <= y && y <= z {
		result = x;
	} else if x <= z && z <= y {
		result = x;
	} else if y <= x && x <= z {
		result = y;
	} else if y <= z && z <= x {
		result = y;
	} else if z <= x && x <= y {
		result = z;
	} else {
		result = z;
	}

	result
}

pub fn read_text() -> String {
	let mut word = String::new();
	std::io::stdin().read_line(&mut word).ok();
	let answer = word.trim().to_string();

	answer
}

pub fn read_array() -> Vec<char> {
	let array: String = read();
	let chars: Vec<char> = array.trim().chars().collect::<Vec<char>>();
	chars
}

pub fn read<T: FromStr>() -> T {
	let stdin = stdin();
	let stdin = stdin.lock();
	let token: String = stdin
		.bytes()
		.map(|c| c.expect("failed to read char") as char)
		.skip_while(|c| c.is_whitespace())
		.take_while(|c| !c.is_whitespace())
		.collect();
	token.parse().ok().expect("failed to parse token")
}