package main

import . "fmt"

func main() {
	var t,x,a,y,b int
	Scan(&t,&x,&a,&y,&b)
	// T = i * a - j * b + k
	// k = T - i * a + j * b
	// min( i * x + j * y + k )
	// min( i * x + j * y + (T - i * a + j * b) )
	// min( i * (x - a) + j * (y + b) + T )
	ans := int(1e18)
	for j := 0; j <= 1e7+1; j++ {
		tmp := t + j * b
		if tmp < 0 {
			continue
		} else if tmp == 0 {
			ans = min(ans, j*y)
		} else if tmp < a || x >= a {
			ans = min(ans, j*y + tmp)
		} else {
			i := tmp / a
			k := tmp % a
			ans = min(ans, i*x+j*y+k)
		}
	}
	Println(ans)
}