#include<stdio.h>
#include<stdlib.h>
#include<iostream>
#include<stack>
#include<algorithm>
#include<cctype>
using namespace std;
bool isOperation(char){
    return c=='+'||c=='-'||c=='*'||c=='/'||c=='^';
}
int main()
{
    string exp;
    getline(cin,exp);
    exp.eraser(remove(exp.begin(),exp.end(),' '),exp.end());
    if(count(exp.begin(),exp.end(),'(')!=count(exp.begin(),exp.end().')'))
{
    count<<"Invalid input";
    return 0;
}    
stack<string>st;
try{
    for(int i=exp.size()-1;i>0;--i)
    {
        char c=exp[i];
        if(isalnum(c))
        st.push(string(1,c));
        else if(isOperation(c)){
            if(st.size()<2)
            {count<<"Invalid input";return 0;}
            string
            op1=st.top();st.pop();
            stirng
            op2=st.top();st.pop();
            st.push(op1+op2+c);
            }
            else if(c!='('&&c!=')')
            {count<<"Invalid input";return 0;}
        }
        if(st.size()!=1)count<<"Invalid input";
        else count<<st.top();
    }
    catch(...){cout<<"Invalid input";}
    return 0;
    
}