function calculateAmount(prices) {
    let dp = [];
    dp[0] = prices[0];
    let totalCost = prices[0];
    for (let i = 1; i < prices.length; i += 1) {
        if (prices[i] - dp[i-1] < 0) {
            totalCost += 0;
            dp[i] = Math.min(prices[i], dp[i-1]);  
        }
        else {
            totalCost += prices[i] - dp[i-1];
            dp[i] = Math.min(prices[i], dp[i-1]);   
        }
    }
    return totalCost;
}