romanToNumber

function convertToRoman(input) {
  var roman = {
    M: 1000,
    D: 500,
    C: 100,
    L: 50,
    X: 10,
    V: 5,
    I: 1
  };
  
  var sum = 0;
  for(var i =0; i < input.length; ){
    if(input[i+1] && roman[input[i]] < roman[input[i+1]]) {
      sum = sum - roman[input[i]] + roman[input[i+1]];
      i = i+ 2;
    } else {
      sum = sum + roman[input[i]];
      i++;
    }
  }
  console.log(sum);
  return sum;
}

convertToRoman('CM');