competitive-programming/solved-uva/11466.cpp at master · the-redback/competitive-programming · GitHub

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/**
 *                                   ____
 *       ____ ___  ____ ________  __/ __/
 *      / __ `__ \/ __ `/ ___/ / / / /_
 *     / / / / / / /_/ / /  / /_/ / __/
 *    /_/ /_/ /_/\__,_/_/   \__,_/_/
 *
 *    @link : https://the-redback.com
 */
#include <bits/stdc++.h>
using namespace std;
#define inf       HUGE_VAL
#define mem(a, b) memset(a, b, sizeof(a))
#define MAX       9999999
bool pr[MAX + 7];
vector<int> v;
void sieve(int n) {
    long long i, j;
    for (i = 4; i < n; i += 2) pr[i] = 1;
    for (i = 3; i < n; i += 2)
        if (!pr[i])
            for (j = i * i; j < n; j += 2 * i) pr[j] = 1;
    for (i = 2; i < n; i++)
        if (!pr[i]) v.push_back(i);
}

long long divisor(long long n) {
    if (n < 0) n *= -1;
    long long res;
    int flag = 0, i, j;
    int sz = v.size();
    for (j = 0; j < sz && v[j] * v[j] <= n; j++) {
        i = v[j];
        if (!(n % i)) {
            // cout<<i<<" ";
            flag++;
            res = i;
        }
        while (!(n % i)) {
            n /= i;
        }
        if (n == 1) break;
    }
    if (n > 1) {
        flag++;
        res = n;
    }
    if (flag <= 1) return -1;
    return res;
}

int main() {
    sieve(MAX + 1);
    int tc, t = 1;
    long long K;
    // scanf("%d",&tc);
    while (~scanf("%lld", &K)) {
        if (K == 0) return 0;
        K = divisor(K);
        printf("%lld\n", K);
    }
    return 0;
}