#include <bits/stdc++.h>

int ri() {
	int n;
	scanf("%d", &n);
	return n;
}


int main() {
	int a = ri();
	int b = ri();
	int c = ri();
	int d = ri();
	int e = ri();
	int x = d;
	int res = 0;
	for (int i = 0; i < a * (b - c); i++) {
		res += x;
		
		if ((i + 2) % 10 == 0 && e <= x) x -= e;
	}
	printf("%d\n", res);
	return 0;
}