diff --git a/.ACM-Templates/isPrime.cpp b/.ACM-Templates/isPrime.cpp
new file mode 100644
index 0000000..04ac238
--- /dev/null
+++ b/.ACM-Templates/isPrime.cpp
@@ -0,0 +1,20 @@
+//Written by Coffee. 判断素数  
+bool isPrime(int num)  
+{  
+    if (num == 2 || num == 3)  
+    {  
+        return true;  
+    }  
+    if (num % 6 != 1 && num % 6 != 5)  
+    {  
+        return false;  
+    }  
+    for (int i = 5; i*i <= num; i += 6)  
+    {  
+        if (num % i == 0 || num % (i+2) == 0)  
+        {  
+            return false;  
+        }  
+    }  
+    return true;  
+}