#include <iostream>
#include <fstream>
#include <string>



using namespace std;
// Sign = + | -
bool isSign(const char* number, unsigned int& ptr)
{
    if (number[ptr] == '+' || number[ptr] == '-' )
    {
        ++ptr;
        return true;
    }

    return false;
}

//isDigit = 0 | 1 | 2 | 3 | 4 | 5 | 6 |7 | 8 | 9
bool isDigit(const char* number, unsigned int& ptr)
{
    if (number[ptr] >= '0' && number[ptr] <= '9')
    {
        ++ptr;
        return true;
    }
    return false;
}

//unsigned number = <Digit> | <Digit> <unsigned number>
bool unsigned_number(const char* number, unsigned int& ptr)
{

    if (!isDigit(number, ptr))
        return false;
    return unsigned_number(number, ptr);
}

//order = E <Sign> <unsigned number>
bool order(const char* number, unsigned int& ptr)
{
    if (number[ptr - 1] == '.' || number[ptr] != 'E' || !isSign(number, ++ptr) || number[ptr] == '\0' )
        return false;

    unsigned_number(number, ptr);
    if (number[ptr] == '\0')
        return true;

    return false;
}

//mantiss = <unsigned_number>.<unsigned number> | <unsigned_number>
bool mantiss(const char* number, unsigned int& ptr)
{
    if (!unsigned_number(number, ptr) && number[ptr] == '.' && ptr!=0)
        return !(unsigned_number(number, ++ptr));
    return true;
}

//<isReal> ::= <matiss> <order> || <sign> <mantis> <order>
bool isReal(const char* number, unsigned int ptr = 0) // n
{
    if (mantiss(number, ptr) && order(number, ptr) && *number != '\0')
        return true;
    else if (isSign(number, ptr) && mantiss(number, ptr) && order(number, ptr) && *number != '\0')
        return true;
    else
    return false;
}



const char* FLIE_NOT_OPEN = "Could not open file!";
int main()
{
    try
    {
        fstream fin;
        string path = "input.txt";
        fin.open(path, fstream::in);
        if (!fin.is_open()) throw FLIE_NOT_OPEN;
        char* num = new char[255];
        fin >> num;
        cout << ((isReal(num)) ? "true" : "false") << endl;
        fin.close();
        delete[] num;
        return 0;
    }
    catch (const char* err)
    {
        cerr << endl << err << endl;
        return -1;
    }
}