diff --git a/QUSTOJ/1713.cpp b/QUSTOJ/1713.cpp
new file mode 100644
index 0000000..1b6c85b
--- /dev/null
+++ b/QUSTOJ/1713.cpp
@@ -0,0 +1,125 @@
+#include <cstdio>
+#include <cstring>
+#include <cstdlib>
+#include <algorithm>
+using namespace std;
+
+int node[20000000]= {0};
+
+int require(int targetleft,int targetright,int cnode,int leftbound,int rightbound)
+{
+    if(targetleft<=leftbound&&targetright>=rightbound)
+    {
+        return node[cnode];
+    }
+    if(targetright<leftbound||targetleft>rightbound)
+    {
+        return 0;
+    }
+    int a=require(targetleft,targetright,cnode*2+1,leftbound,(rightbound+leftbound)/2);
+    int b=require(targetleft,targetright,cnode*2+2,(leftbound+rightbound)/2+1,rightbound);
+    return max(a,b);
+}
+
+void special(int q)
+{
+    /// n==1
+    int x=0;
+    scanf("%d",&x);
+    for(int i=0; i<q; i++)
+    {
+        char c[4];
+        c[0]=c[1]=c[2]=c[3]=0;
+        int a,b;
+        scanf("%s %d %d",c,&a,&b);
+        switch(c[0])
+        {
+        case 'Q':
+            printf("%d\n",x);
+            break;
+        case 'U':
+            x=b;
+            break;
+        }
+    }
+}
+
+int main()
+{
+    int n,m;
+    while(scanf("%d %d",&n,&m)==2)
+    {
+        memset(node,0,20000000);
+
+        if(n==1)
+        {
+            special(m);
+            ///printf("XXXX\n");
+            return 0;
+        }
+
+        int realn=1;
+        while(realn<n) realn*=2;
+        for(int k=realn-1; k<=realn+n-2; k++)
+        {
+            scanf("%d",&node[k]);
+        }
+        /// build tree
+        int lastcur=realn;
+        int cur=lastcur/2-1;
+        while(cur>0)
+        {
+            for(int toadd=0; toadd<cur+1; toadd++)
+            {
+                node[cur+toadd]=max(node[2*(cur+toadd)+1],node[2*(cur+toadd)+2]);
+            }
+            lastcur=cur+1;
+            cur=lastcur/2-1;
+        }
+        node[0]=max(node[1],node[2]);
+        for(int query=0; query<m; query++)
+        {
+            char c[4];
+            c[0]=c[1]=c[2]=c[3]=0;
+            int a,b;
+            scanf("%s %d %d",c,&a,&b);
+            switch(c[0])
+            {
+            case 'U':
+            {
+                node[realn-1+a-1]=b;
+                int cnt=(realn-1+a-1-1)/2;
+                while(cnt>0)
+                {
+                    node[cnt]=max(node[cnt*2+1],node[cnt*2+2]);
+                    cnt=(cnt-1)/2;
+                }
+                node[0]=max(node[1],node[2]);
+            }
+            break;
+            case 'Q':
+            {
+                if(a==b)
+                {
+                    printf("%d\n",node[realn-1+a-1]);
+                }
+                else
+                {
+                    if(b<a)
+                    {
+                        int tmp=a;
+                        a=b;
+                        b=tmp;
+                    }
+                    int ans=require(a-1,b-1,0,0,realn-1);
+                    printf("%d\n",ans);
+                }
+            }
+            break;
+            default:
+                printf("ERROR\n");
+            }/// end of switch
+        }
+    }
+    return 0;
+}