#include<bits/stdc++.h>
#define int long long
#define ist istringstream
using namespace std;
string ex;
stack<int>st;
int l; 
char zf;
int solve() 
{
	cin>>ex;
	l=ex.size();
	int ll=l-1;
	ist iss(ex);
	while(ll--)
	{
		iss>>zf;
		if(zf=='.')
		{
			continue;
		}
		else if(isdigit(zf)!=0)
		{
			st.push(zf-'0');
		}
		else
		{
			int n2=st.top();
			st.pop();
			int n1=st.top();
			st.pop();
			switch(zf)
			{
				case '+':
					st.push(n1+n2);
					break;
				case '-':
					st.push(n1-n2);
					break;
				case '*':
					st.push(n1*n2);
					break;
				case '/':
					st.push(n1/n2);
					break;
					
			}
		}
	}
	return st.top();
}
signed main()
{
	cout<<solve();
 	return 0;
}

why? 测试信息