Termination Upon Esc

#include "iostream"
#include "conio.h"
using namespace std;
void main ()
{
    signed int a=0;
    do
    {
        a++;
        cout<<a<<endl;

    }
    while (a>-1);
    getch();
}

I want this loop program to terminate upon pressing esc key. How do I do that /prog/? Halp me pls.