JS POWER

const readline = require('readline');
const rl = readline.createInterface({
input: process.stdin,
output: process.stdout
});

var c,x,y,z,m,s,f,e,t;

rl.on('line', function(line){
var arr = line.split(' ');
c = Number(arr[0]);
x = Number(arr[1]);
y = Number(arr[2]);
z = Number(arr[3]);
m = Number(arr[4]);
s = Number(arr[5]);
f = Number(arr[6]);
e = Number(arr[7]);
t = Number(arr[8]);
});

rl.on('close', function() {
// war strategy
var war = t + m * Math.ceil( (e+1) * f / s );

// money strategy
// k = num of extra warehouses needed to store requires ammount
var k = Math.max(0, Math.ceil( (c - x) / z ));
var money = Math.ceil( ( k * y + c ) / s ) * m;

console.log(Math.min(war, money));
});