#include <iostream>

char *x = "";

int parse();
int convert();
int calc();
int uInt();
int equalSign();
int sign();
int term();

int main()
{
    if(parse())
    {
        std::cout << "successful";
    }
    else
        std::cout << "unsuccessful";
}
int parse()
{
    if(uInt())
    {
        if(sign())
        {
            if(uInt())
            {
                if(equalSign())
                {
                    return 1;
                }
                else{
                    std::cout << "Equal sign expected\n";
                    return 0;
                    }
            }
            else
            {
                std::cout << "Expected digit\n";
                return 0;
            }
        }
        else
        {
            std::cout << "Operation sign expected\n";
            return 0;
        }
    }
    else
    {
        std::cout << "Expected digit\n";
        return 0;
    }
}


int uInt()
{
    if(*x>='0' && *x<='9')
    {
        x++;
        uInt();
        return 1;
    }
}

int sign()
{
    if(*x=='+' || *x=='/' || *x=='*' ||*x=='-')
    {
        x++;
        return 1;
    }
    else
    {

        return 0;
    }
}

int equalSign()
{
    if (*x == '=')
    {
        return 1;
    }
    else
        return 0;
}