#include <stdio.h>
#include <stdlib.h>
#include <iostream>
#include <math.h>
#include <string>

using namespace std;

template <class T>
bool isPrime(T n) //test if prime
{
    for(T i(2); i <= sqrt(n); ++i)
        if (n % i == 0)
            return false;
    return true;
}

int getHex(string hexstr) { //hexadecimal to decimal
    return (int)strtol(hexstr.c_str(), 0, 16);
}

string decToHexa(int n) { //decimal to hexadecimal
    char hexaDeciNum[16];

    int i = 0;
    while(n!=0){
        int temp  = 0;
        temp = n % 16;
        if(temp < 10)
        {
            hexaDeciNum[i] = temp + 48;
            i++;
        }
        else
        {
            hexaDeciNum[i] = temp + 55;
            i++;
        }

        n = n/16;
    }

	string str = "";
    for(int j=i-1; j>=0; j--){
		str+=hexaDeciNum[j];
	}
	while(str.size()<2){
		str="0"+str;
	}
	return str;
}

int main(int argc, char *argv[]){

	double clos = 256*2; //The value can not be any further than 442 units. 3 dimensional distance: sqrt( 255^2*3)

	for(int a=0;a<256;a++){	// a=red b=green c=blue
		for(int b=0;b<256;b++){
			for(int c=0;c<256;c++){

    			string str; //concate rgb hexadecimals
				str+=decToHexa(a);
				str+=decToHexa(b);
				str+=decToHexa(c);

				int cand = getHex(str); //convert concated hex value to dec
				if(isPrime(cand)){ //test if it is a prime

					int r2=getHex("C9"); //convert the picked color into decimals
					int g2=getHex("00");
					int b2=getHex("BD");

					int r1 = a; //compare current color a,b,c with picked color
					int g1 = b;
					int b1 = c;

					float d=pow( pow((r2-r1),2) + pow((g2-g1),2) + pow((b2-b1),2) , 0.5 ); //distance
					if(d<=clos){ //If the currently compared color is closer to the picked one
						clos=d; //Mark color to be closest to the picked color
						cout << "Closest: " << cand << " Hex: " << str << " Distance: " << d << "\n"; //print out values
					}
				}

			}
		}
	}

}