Almost Prime

26A.cpp

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+//4240326   Aug 7, 2013 5:13:59 PM	fuwutu	 26A - Almost Prime	 GNU C++0x	Accepted	 30 ms	 0 KB
+#include <cstdio>
+
+int main()
+{
+    int n, amount(0);
+    scanf("%d", &n);
+
+    bool b[3001] = {false};
+    int pfactors[3001] = {0};
+    for (int i = 2; i <= n; ++i)
+    {
+        if (!b[i])
+        {
+            for (int j = i + i; j <= n; j += i)
+            {
+                b[j] = true;
+                pfactors[j] += 1;
+            }
+        }
+
+        if (pfactors[i] == 2)
+        {
+            amount += 1;
+        }
+    }
+    printf("%d\n", amount);
+    return 0;
+}