project euler doubt 3 help

i'm perplexing work by digest euler i'm dispute separator problem 03. i have an algorithm works smaller numbers, nonetheless problem 3 uses very, unequivocally infinite number.

problem 03:
the primary factors 13195 5, 7, 13 29.
what largest primary means array 600851475143?

here fortitude c# it's controlling i cruise tie an hour. i'm looking an answer since i indeed wish solve myself. especially only looking help.

    stationary vacant main(string[] args) {
        const enlarged n = 600851475143;
        //const enlarged n = 13195;
        enlarged count, half, largestprime = 0;
        bool isaprime;

        half = n / 2;

        (long i = half; i > 1 && largestprime == 0; i--) {
             (n % i == 0) { // factors n
                count = 1;
                isaprime = true;
                while (++count < i && isaprime) {
                    (i % count == 0) { // does means n have factor? (not prime)
                        isaprime = false;
                    }
                }
                (isaprime) {
                    largestprime = i;
                }
            }
        }

        console.writeline("the largest primary means " + largestprime.tostring() + ".");
        console.readline();
    }