https://www.luogu.com.cn/problem/P1449

//自认为代码清晰，需要注意的地方只有"-"、"/"时y,z的顺序即可
#include<bits/stdc++.h>
using namespace std;
const int N = 100010;
typedef long long LL;
typedef list<int>::iterator Iter;
list<int> L;
deque<int> dq;
queue<int> q;
stack<int> s;
vector<int> a(N + 1, 0);
int main(){
    ios::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
    char ch;
    int x = 0, y = 0, z = 0, ans = 0;
    while (ch != '@') {
        ch = getchar();
        if (ch == '.') {s.push(x);x = 0;}
        else if (ch == '*') {y = s.top();s.pop();z = s.top();s.pop();ans = y * z;s.push(ans);}
        else if (ch == '/') {y = s.top();s.pop();z = s.top();s.pop();ans = z / y;s.push(ans);}
        else if (ch == '+') {y = s.top();s.pop();z = s.top();s.pop();ans = y + z;s.push(ans);}
        else if (ch == '-') {y = s.top();s.pop();z = s.top();s.pop();ans = z - y;s.push(ans);}
        else x = x * 10 + (ch - '0');
    }
    cout << s.top();
    return 0;
}