#include <iostream>
#include <string>
#include <stack>

void to_postfix(std::stack<char>&, std::string&, std::string&);
bool is_operator(char);
int priority(char);

int main(int argc, char *argv[])
{
    if (argc != 2) {
        std::cerr << "Args: String_to_postfix" <<std::endl;
        return 1;
    }
    std::stack<char> expression;
    std::string my_postfix;
    std::string my_infix = argv[1];
    to_postfix(expression, my_postfix, my_infix);
    std::cout << my_postfix << std::endl;
    return 0;
}

void to_postfix(std::stack<char>& s, std::string& postfix, std::string& infix) {
    unsigned int i = 0;
    s.push('(');
    infix = infix + ')';
    while (!s.empty()) {
       if (infix[i] >= '0' && infix[i] <= '9')
           postfix.append(1, infix[i]);
       else if (infix[i] == '(')
           s.push(infix[i]);
       else if (is_operator(infix[i])) {
           while (priority(infix[i]) >= priority(s.top())) {
               postfix.append(1, s.top());
               s.pop();               
           }
           s.push(infix[i]);
       }
       else if (infix[i] == ')') {
           while (s.top() != '(')
               if (is_operator(s.top())) {
                   postfix.append(1, s.top());
                   s.pop();
               }
           s.pop();
       }
       i++;
    }
}

int priority(char op)
{
    if(op == '+' || op == '-')
        return 1;
    else if(op == '*' || op == '/')
        return 2;
    else if(op == '%' || op == '^')
        return 3;
    else
        return 4;
}

bool is_operator(char op)
{
    if(op == '+' || op == '-' || op == '*' || 
    op == '/' || op == '^' || op == '%')
        return true;
    else
        return false;
}