Project Euler Problem 3

I keep getting an error but I think its a stupid mistake which I cannot find o.o just started so... any help is appreciated.
Problem :
The prime factors of 13195 are 5, 7, 13 and 29.

What is the largest prime factor of the number 600851475143 ?
found it just had to add ULL suffix
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#include <iostream>

using namespace std;
bool isprime(long long n);
long long fbp (long long n);

int main()
{
//=============================================================================
    /* Euler 1

    sum=0;
    for(int i=0;i<1000;i++)
    {
        if(i%3==0 ||i%5==0 )
        {
            sum=sum+i;
        }

    }
    cout<< sum;
    */
//=============================================================================
//=============================================================================
/*  Euler 2
    int current, next, total,temp;
    current =1;
    next = 2;
    total=0;
    while(total<4e6)
    {
        if(current%2==0)
        {
            total+=current;
        }
        temp= current;
        current = next;
        next = temp+current;
    }




    cout << total << endl;
*/
//=============================================================================
unsigned long long lpf = 600851475143;
cout << fbp(lpf) << endl;

    return 0;
}
long long fbp(long long  n)
{
    long long factor;
    for(long long i = 3; i <= n; i += 2)
    {
        if(n % i == 0)
        {
            if(isprime(i))
            {
                factor = i;
                cout << factor << endl;
            }
        }
    }
    return factor;
}

bool isprime(long long  n)
{
    if(n%2== 0)
    {
        return 0;
    }
    for(long long i = 3; i <= ((n/2)+1);i +=2)
    {
        if(n%i== 0)
        {
            return 0;
        }
    }
    return 1;
}
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