#include <iostream>
using namespace std;
 
int main() {
	const long numm = 600851475143;
long newnumm = numm;
long largestFact = 0;
 
int counter = 2;
while (counter * counter <= newnumm) {
    if (newnumm % counter == 0) {
        newnumm = newnumm / counter;
        largestFact = counter;
    } else {
        counter++;
    }
}
if (newnumm > largestFact) { // the remainder is a prime number
    largestFact = newnumm;
}
cout<<largestFact<<endl;
	// your code goes here
	return 0;
}

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