add problem

grub/truculencia-2019-02/nt/stars/README.md

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+# [Stars](https://www.urionlinejudge.com.br/judge/pt/problems/view/1233)

grub/truculencia-2019-02/nt/stars/main.cpp

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+#include <bits/stdc++.h>
+
+using namespace std;
+
+const long long MAX = pow(2, 16);
+
+list<long long> primes;
+
+void generate_primes() {
+    bitset<MAX+1> sieve;
+    sieve.set(false);
+
+    for (long long i = 2; i <= MAX; i++) {
+        if (!sieve[i]) {
+            primes.push_back(i);
+
+            for (long long j = 0; i*i + j*i <= MAX; j++) {
+                sieve[j*i+i*i] = true;
+            }
+        }
+    }
+}
+
+
+int main(void) {
+    generate_primes();
+
+    long long n;
+    long long result;
+
+    while (~scanf("%lld", &n)) {
+        result = n;
+        bool prime = true;
+
+        for(list<long long>::iterator it = primes.begin(); it != primes.end() && *it <= n; it++) {
+            if (n % *it == 0) {
+                result /= *it;
+                result *= *it - 1;
+
+                while (n % *it == 0) n /= *it;
+            }
+        }
+
+        if (n > 1) {
+            result /= n;
+            result *= n - 1;
+        }
+
+        long long n_coprimes = result;
+        long long n_stars    = n_coprimes/2;
+
+        printf("%lld\n", n_stars);
+    }
+
+    return 0;
+}
+