string intToRoman(int num) {
vector<int> romans {1000, 900, 500, 400, 100, 90, 50, 40, 10, 9, 5, 4, 1};
vector<string> letters {"M", "CM", "D", "CD", "C", "CX", "L", "XL", "X","IX", "V", "IV", "I"};
std::string roman="";
auto lx = letters.begin();
auto r = romans.begin();
for (; r != romans.end() && lx != letters.end(); )
{
int rom = *r;
string let = *lx;
int div = num/rom;
if (div) { roman += let; num -= rom; }
else { r++; lx++; }
}
return roman;