function Main(input) {
    let src = input.replace("\n", "").split(" ");
    let a = parseInt(src[0]);
    let b = parseInt(src[1]);
    let c = parseInt(src[2]);
    let d = parseInt(src[3]);
    let e = parseInt(src[4]);
    let n = a * (b - c);
    let ans = 0;
    for (let i = 1; i <= n; i++) {
        if (i % 10 == 0 && d >= e) {
            d -= e;
        }
        ans += d;
    }
    console.log(ans);
}
Main(require("fs").readFileSync("/dev/stdin", "utf8"));