为什么在主线程中收到CMException错误？

这是一个允许用户输入年份并以罗马数字返回相应年份的程序。我可以编译它而没有任何错误，但是当我运行它时，它会出错。

这样运行该程序时出现错误，

该程序的代码是

import java.io.*;
public class RomanCal {
public static void main(String args[])throws IOException{
    int year;
    BufferedReader input = new BufferedReader(new InputStreamReader(System.in));

    System.out.print("Enter a year to convert : ");//asking for input
    year = input.read();

    start(year);
}

public static void start(int year){
    String full = Integer.toString(year);//full year is converted to a String
    String check = full.substring(0,1);

    switch (check){//checking the first number
    case "1" : System.out.println("M");
    break;
    case "2" : System.out.println("MM");
    break;
    default : System.out.println("Invalid Year");
     }

    check = full.substring(1,2);

    switch (check){//checking the second number
    case "0" : 
        check = full.substring(2,3);
        switch (check){//check the third number if second is zero
        case "0" :
            check = full.substring(3,4);
            switch (check){//check the fourth number if third is zero
            case "1" : System.out.print("I");
            break;
            case "2" : System.out.print("II");
            break;
            case "3" : System.out.print("III");
            break;
            case "4" : System.out.print("IV");
            break;
            case "5" : System.out.print("V");
            break;
            case "6" : System.out.print("VI");
            break;
            case "7" : System.out.print("VII");
            break;
            case "8" : System.out.print("VIII");
            break;
            case "9" : System.out.print("IX");
            break;
            }
            break;



        case "1" : System.out.print("X");
        break;
        case "2" : System.out.print("XX");
        break;
        case "3" : System.out.print("XXX");
        break;
        case "4" : System.out.print("XL");
        break;
        case "5" : System.out.print("L");
        break;
        case "6" : System.out.print("LX");
        break;
        case "7" : System.out.print("LXX");
        break;
        case "8" : System.out.print("LXXX");
        break;
        case "9" : System.out.print("XC");
        break;
        }
        break;



    case "1" : System.out.print("C");
    break;
    case "2" : System.out.print("CC");
    break;
    case "3" : System.out.print("CCC");
    break;
    case "4" : System.out.print("CD");
    break;
    case "5" : System.out.print("D");
    break;
    case "6" : System.out.print("DC");
    break;
    case "7" : System.out.print("DCC");
    break;
    case "8" : System.out.print("DCCC");
    break;
    case "9" : System.out.print("CM");
    break;
    }


    check = full.substring(3,4);

    switch (check){//check the fourth number
    case "1" : System.out.print("I");
    break;
    case "2" : System.out.print("II");
    break;
    case "3" : System.out.print("III");
    break;
    case "4" : System.out.print("IV");
    break;
    case "5" : System.out.print("V");
    break;
    case "6" : System.out.print("VI");
    break;
    case "7" : System.out.print("VII");
    break;
    case "8" : System.out.print("VIII");
    break;
    case "9" : System.out.print("IX");
    break;
    }





}


}