#include <iostream>
#include <conio.h>

unsigned fact( unsigned n )
{
    return ( n == 0 || n == 1 ) ? 1 : n * fact( n - 1 );
}

int main()
{

    double arr[] = { 0.0, 10.0, 3.0, 7.8,13.4 };
    size_t n = sizeof(arr) / sizeof(arr[0]);

    double result;
    bool has_result = false;

    for( unsigned i = 0; i < n; ++i )
    {
        if( (i+1) < arr[i] && arr[i] < fact(i) )
        {
            if( has_result ) result *= arr[i];
            else
            {
                has_result = true;
                result = arr[i];
            }
        }
    }

    if( has_result )
    {
        result = 1 / result;
        std::cout << "Result: " << result << std::endl;
    }
    else
    {
        std::cout << "Result does not exist!\n";
    }

    _getch();
    return 0;
}