diff --git a/HDOJ/5879_zsd201531107026.cpp b/HDOJ/5879_zsd201531107026.cpp
new file mode 100644
index 0000000..181c5fd
--- /dev/null
+++ b/HDOJ/5879_zsd201531107026.cpp
@@ -0,0 +1,33 @@
+#include<cstdio>
+#include<cstring>
+#include<algorithm>
+#include<cmath>
+using namespace std;
+
+const int N = 1e6 + 5;
+
+char a[N];
+double sum[N];
+
+void yu()
+{
+    for(int i = 1 ; i < N ; i++){
+        sum[i] = sum[i - 1] + (double)1/i/i;
+    }
+}
+int main()
+{
+    yu();
+    while(~scanf("%s",a)){
+        int l = strlen(a);
+        if(l >= 7) printf("%.5lf\n",sum[1000000]);
+        else{
+            int n = 0;
+            for(int i = 0 ; i < l ; i++){
+                n = n * 10 + a[i] - '0';
+            }
+            printf("%.5lf\n",sum[n]);
+        }
+    }
+    return 0;
+}