function romanToInt(s) {
 const d = {I: 1, V: 5, X: 10, L: 50, C: 100, D: 500, M: 1000};
 let summ = 0;
 const n = s.length;
 let i = 0;
 while (i < n) {
 if(i > 1 && d[s[i - 2]] < d[s[i - 1]] && d[s[i]] <= d[s[i - 1]]) {
 throw new Error(`Invalid Roman numeric sequence ${s}`);
 }
 if (i < n - 1 && d[s[i]] < d[s[i + 1]]) {
 summ += d[s[i + 1]] - d[s[i]];
 i += 2;
 } else {
 summ += d[s[i]];
 i++;
 }
 }
 return summ;
}
console.log(romanToInt('IIXX'));
console.log(romanToInt('MMD'));