Largest prime factor

Problem Description
Everybody knows any number can be combined by the prime number.
Now, your task is telling me what position of the largest prime factor.
The position of prime 2 is 1, prime 3 is 2, and prime 5 is 3, etc.
Specially, LPF(1) = 0.

Input
Each line will contain one integer n(0 < n < 1000000).

Output
Output the LPF(n).

Sample Input
1
2
3
4
5

Sample Output
0
1
2
1
3

 #include<iostream>
#include<cmath>
using namespace std;

bool isPrime(int n)
{
    for (int i = 2; i <= sqrt(n); ++i)
    {
        if (n % i == 0)
            return false;
    }
    return true;
}

int main()
{
    int num;
    while(cin >> num)
    {
        if (isPrime(num))
        {
            int pos = 0;
            if (num > 1)
                pos = 1;
            for (int i = 3; i <= num; i += 2)
            {
                if (isPrime(i))
                    pos++;
            }
            cout << "position is:" << pos << endl;
        }
        else
            cout << "position is:" << 1 <<endl;
    }
    return 0;
}

不是素数的就默认position为1