Надо чтобы пользователь вводил время только в секундах,вместо часов,минут и секунд

#include <iostream>
#include <conio.h>
using namespace::std;
int main()
{
    const int time = 86400;
    int begin_hours, begin_min, begin_sec;
    int end_hours, end_min, end_sec;
    cout << "Enter h,min,sec" << endl;
    cin >> begin_hours >> begin_min >> begin_sec;
 
    double tmp = begin_hours * 3600 + begin_min * 60 + begin_sec;
    tmp = time - tmp;
    end_hours = tmp / 3600;
    end_min = tmp / 60 - end_hours * 60;
    end_sec = tmp - end_min * 60 - end_hours * 3600;
    cout << "before the end of the day left " << end_hours << " h " << end_min << " min " << end_sec << " sec" << endl;
}

cout << "Enter sec" << endl;
cin >> begin_sec;
 
double tmp = begin_sec;
tmp = time - tmp;
end_hours = tmp / 3600;
end_min = tmp / 60 - end_hours * 60;
end_sec = tmp - end_min * 60 - end_hours * 3600;
cout << "before the end of the day left " << end_hours << " h " << end_min << " min " << end_sec << " sec" << endl;

#include <iostream>
#include <conio.h>
using namespace::std;
int main()
{
cout << "Enter sec" << endl;
cin >> begin_sec;
double tmp = begin_sec;
tmp = time - tmp;
end_hours = tmp / 3600;
end_min = tmp / 60 - end_hours * 60;
end_sec = tmp - end_min * 60 - end_hours * 3600;
cout << "before the end of the day left " << end_hours << " h " << end_min << " min " << end_sec << " sec" << endl;
}

#include <iostream>
#include <conio.h>
using namespace::std;
int main()
{
const int time = 86400;
int begin_sec;
int end_hours, end_min, end_sec;
 
cout << "Enter sec" << endl;
cin >> begin_sec;
 
double tmp = begin_sec;
tmp = time - tmp;
end_hours = tmp / 3600;
end_min = tmp / 60 - end_hours * 60;
end_sec = tmp - end_min * 60 - end_hours * 3600;
cout << "before the end of the day left " << end_hours << " h " << end_min << " min " << end_sec << " sec" << endl;
}