Postfix Notation Yardim

import java.io.BufferedReader; 
  import java.io.InputStreamReader; 
  import java.util.NoSuchElementException; 
    
  interface Stack<E> { 
    
      // The elements of the Stack are any kind of objects 
    
      // Access methods: 
    
      public boolean isEmpty (); 
      	// Returns true only if the stack is empty. 
    
      public E peek (); 
      	// Returns the element on the top od the stack. 
    
      // Transformation methods: 
    
      public void clear (); 
      	// Clears the stack. 
    
      public void push (E x); 
      	// Adds x on the top of the stack. 
    
      public E pop (); 
      	// Removes and returns the element on the top. 
  } 
    
  class ArrayStack<E> implements Stack<E> { 
      private E[] elems; 
      private int depth; 
    
      @SuppressWarnings("unchecked") 
      public ArrayStack (int maxDepth) { 
          // Creating new empty stack 
          elems = (E[]) new Object[maxDepth]; 
          depth = 0; 
      } 
    
    
      public boolean isEmpty () { 
           // Returns true only if the stack is empty. 
    
          return (depth == 0); 
      } 
    
    
      public E peek () { 
          // Returns the element on the top od the stack. 
          if (depth == 0) 
              throw new NoSuchElementException(); 
          return elems[depth-1]; 
      } 
    
    
      public void clear () { 
          // Clears the stack. 
          for (int i = 0; i < depth; i++)  elems[i] = null; 
          depth = 0; 
      } 
    
    
      public void push (E x) { 
          // Adds x on the top of the stack. 
          elems[depth++] = x; 
      } 
    
    
      public E pop () { 
          // Removes and returns the element on the top. 
          if (depth == 0) 
              throw new NoSuchElementException(); 
          E topmost = elems[--depth]; 
          elems[depth] = null; 
          return topmost; 
      }     
    
  } 
    
    
  public class PostFixEvaluation { 
    
    
  	static int evaluatePostfix(char [] izraz, int n) 
      { 
          int maxDepth=izraz.length; 
          ArrayStack<Character> e = new ArrayStack(n); 
      	char ch,res; 
          int op1,op2,result=0; 
          int i=0; 
          while(i<n) 
          { 
             if(Character.isDigit(izraz[i])) 
             { 
                ch=izraz[i]; 
                e.push(ch);  
             } 
              else 
             { 
                 ch=izraz[i]; 
                 op1 =(int)e.pop(); 
           	   op2 =(int)e.pop(); 
                 if(ch=='+') 
                 { 
                 result=op1+op2;                
                 } 
                  if(ch=='-') 
                 { 
                 result=op1-op2;                
                 } 
                  if(ch=='/') 
                 { 
                 result=op1/op2;                
                 } 
                  if(ch=='*') 
                 { 
                 result=op1*op2;                
                 } 
                   res=(char)result; 
                     e.push(res); 
    
             } 
              i++; 
    
          } 
          return result; 
      } 
    
    
  	public static void main(String[] args) throws Exception{ 
    
          BufferedReader br = new BufferedReader(new InputStreamReader(System.in)); 
    
          String expression = br.readLine(); 
          char exp[] = expression.toCharArray(); 
    
          int rez = evaluatePostfix(exp, exp.length); 
          System.out.println(rez); 
    
          br.close(); 
    
  	} 
    
  }