diff --git a/QUSTOJ/1721.c b/QUSTOJ/1721.c
new file mode 100644
index 0000000..5fdfd82
--- /dev/null
+++ b/QUSTOJ/1721.c
@@ -0,0 +1,37 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+//Written by Kiritow. 求最大公约数
+long gcd(long a,long b)
+{
+	if(a==0||b==0)
+	{
+		if(a+b==0)
+		{
+			return 0;
+		}
+		return (a==0)?b:a;
+	}
+
+	while(a!=b)
+	{
+		if(a>b)
+		{
+			a=a-b;
+		}
+		else
+		{
+			b=b-a;
+		}
+	}
+	return a;
+}
+
+int main()
+{
+    int a,b;
+    scanf("%d%d",&a,&b);
+    int ans=gcd(a,b);
+    printf("%d\n%d\n",ans,a*b/ans);
+    return 0;
+}