diff --git a/QUSTOJ/1775.c b/QUSTOJ/1775.c
new file mode 100644
index 0000000..94bc2fc
--- /dev/null
+++ b/QUSTOJ/1775.c
@@ -0,0 +1,18 @@
+#include <stdio.h>
+#include <stdlib.h>
+
+int main()
+{
+    int n;
+    scanf("%d",&n);
+    double ans=0;
+    if(n%2==1)
+    {
+        for(int k=1;k<=n;k+=2) ans+=1.0/k;
+    }
+    else
+    {
+        for(int k=2;k<=n;k+=2) ans+=1.0/k;
+    }
+    return printf("%f\n",ans),0;
+}