Long time no see

1Y-1H/proglabs/lab6/9.c

@@ -0,0 +1,25 @@
+#include <stdio.h>
+int pr(long long n);
+
+int main() {
+    long long int x,i;
+    printf("Num: ");
+    if(!(scanf("%lld",&x)))return 1;
+
+    for(i = x; i > 1; --i)
+        if(pr(i))
+            printf("%lld\t",i);
+
+    return 0;
+}
+
+int pr(long long n) {
+    if (n < 2) return 0;
+    if (n == 2 || n == 3) return 1;
+    if (n % 2 == 0 || n % 3 == 0) return 0;
+
+    for (long long i = 5; i * i <= n; i += 6) {
+        if (n % i == 0 || n % (i + 2) == 0)
+            return 0;}
+    return 1;
+}