**Simple Python Solution **

x = min(bc,wc+z)
y = min(wc,bc+z)
return (b*x) + (w*y)

def taumBday(b, w, bc, wc, z): if bc == wc: return (b*bc)+(w*wc) else: if min(bc,wc)+z >= max(bc,wc): return (b*bc)+(w*wc) else: if wc < bc: return ((wc+z)*b)+(w*wc) else: return ((bc+z)*w)+(b*bc)

public static long taumBday(long noOfBlackGifts, long noOfWhiteGifts, long blackGiftPrice, long whiteGiftPrice, int conversionCost) {
    if(conversionCost < Math.abs(blackGiftPrice-whiteGiftPrice)) {
        if(blackGiftPrice < whiteGiftPrice) {
            whiteGiftPrice = blackGiftPrice + conversionCost;
        } else if(whiteGiftPrice < blackGiftPrice){
            blackGiftPrice = whiteGiftPrice + conversionCost;
        }
    }
    return (noOfBlackGifts * blackGiftPrice) + (noOfWhiteGifts * whiteGiftPrice);
}

Here is problem solution in Python, Java, C++, C and Javascript - https://programmingoneonone.com/hackerrank-taum-and-bday-problem-solution.html

Here is my simple c++ solution, you can watch the explanation here : https://youtu.be/T9sxEzAbp-M

long taumBday(int b, int w, int bc, int wc, int z) {
    long bp = min(bc, wc + z);
    long wp = min(wc, bc + z);
    return bp * b + wp * w;
}