import java.util.Stack;

public class BasicCalculatorII {

public int calculate(String s) {

Stack<Integer> nums = new Stack<>();

Stack<Character> op = new Stack<>();

char[] ss = s.toCharArray();

int num = 0; boolean flag = false;

for(int i = 0; i < ss.length; i++){

while(i < ss.length && ss[i] == ' ') i++;

while(i < ss.length && Character.isDigit(ss[i])){

num = num * 10 + ss[i] - '0';

i++;

flag = true;

}

if(flag){

nums.push(num);

num = 0;

flag = false;

}

while(i < ss.length && ss[i] == ' ') i++;

if(i < ss.length){

if(ss[i] == '*'){

int num1 = nums.pop();

int num2 = 0;

i++;

while(i < ss.length && ss[i] == ' ') i++;

while(i < ss.length && Character.isDigit(ss[i])){

num2 = num2 * 10 + ss[i] - '0';

i++;

}

i--;

nums.push(num1 * num2);

}else if(ss[i] == '/'){

int num1 = nums.pop();

int num2 = 0;

i++;

while(i < ss.length && ss[i] == ' ') i++;

while(i < ss.length && Character.isDigit(ss[i])){

num2 = num2 * 10 + ss[i] - '0';

i++;

}

i--;

nums.push(num1 / num2);

}else{

op.push(ss[i]);

}

}

}

Stack<Integer> numss = new Stack<>();

while(!nums.isEmpty()) numss.push(nums.pop());

Stack<Character> opp = new Stack<>();

while(!op.isEmpty()) opp.push(op.pop());

while(!opp.isEmpty()){

int num1 = numss.pop();

int num2 = numss.pop();

if(opp.pop() == '+'){

numss.push(num1 + num2);

}else{

numss.push(num1 - num2);

}

}

return numss.pop();

}

public static void main(String[] args) {

BasicCalculatorII calc = new BasicCalculatorII();

System.out.println(calc.calculate("2/2 *3 + 1"));

}

}