python 3:

def calculate(s: str) -> int:
        
    def helper(s: list) -> int:
        stack = []
        sign = '+'
        num = 0

        while len(s) > 0:
            c = s.pop(0)
            if c.isdigit():
                num = 10 * num + int(c)
            if c == '(':
                num = helper(s)

            if (not c.isdigit() and c != ' ') or len(s) == 0:
                if sign == '+':
                    stack.append(num)
                elif sign == '-':
                    stack.append(-num)
                elif sign == '*':
                    stack[-1] = stack[-1] * num
                elif sign == '/':
                    stack[-1] = int(stack[-1] / float(num))  
                elif sign == '^':
                    stack[-1] = int(stack[-1]**num)
                num = 0
                sign = c
            if c == ')': break
        return sum(stack)

    return helper(list(s))

a=input()
print(calculate(a))

//半成品别复制 只是单纯懒得再写一次了
#include<bits/stdc++.h>
using namespace std;
const int N = 1e4 + 10;
string a;
stack<long long> st;
long long sum;
void calc(char ob)
{
	long long a = st.top();
	st.pop();
	long long b = st.top();
	st.pop();
	if(ob == '+') st.push(a + b);
	else if(ob == '-') st.push(a - b);
	else if(ob == '*') st.push(a * b);
	else if(ob == '/') st.push(a / b);
}
int main(){
	getline(cin,a);
	int len = a.size();
	for(int i = 0;i < len;i++)
	{
	
		    if(a[i] == '@') break;
		    if(a[i] >= '0' && a[i] <= '9') 
			    sum = sum * 10 + a[i] - '0';
			else if(a[i] == ' ')
			{
			    st.push(sum);
			    sum = 0;
			}    
			else
			{
				calc(a[i]);
			}
    }
    cout << st.top();
	return 0;
}