diff --git a/OnlineJudges/lydsy/2005.cpp b/OnlineJudges/lydsy/2005.cpp
new file mode 100644
index 0000000..43fcf5a
--- /dev/null
+++ b/OnlineJudges/lydsy/2005.cpp
@@ -0,0 +1,18 @@
+//http://blog.csdn.net/popoqqq/article/details/39924877
+#include <cstdio>
+long long f[100100], ans;
+int main()
+{
+    int m, n, k;
+    scanf("%d%d", &m, &n);
+    k = (m < n ? m : n);
+    for (int i = k; i; i--)
+    {
+        f[i] = 1ll * (m / i) * (n / i);
+        for (int j = 2; j * i <= k; j++)
+            f[i] -= f[i * j];
+        ans += f[i] * (i + i - 1);
+    }
+    printf("%lld", ans);
+    return 0;
+}
\ No newline at end of file
diff --git a/OnlineJudges/lydsy/2173.cpp b/OnlineJudges/lydsy/2173.cpp
new file mode 100644
index 0000000..f50984e
--- /dev/null
+++ b/OnlineJudges/lydsy/2173.cpp
@@ -0,0 +1,12 @@
+#include <cstdio>
+long long f[4];
+int main()
+{
+    f[1] = 1;
+    int n;
+    scanf("%d", &n);
+    for (int i = 2; i <= n; i++)
+        f[i & 3] = ((f[(i - 1) & 3] << 1) + f[(i - 2) & 3]) % 1000000007;
+    printf("%lld", f[n & 3]);
+    return 0;
+}
\ No newline at end of file
diff --git a/OnlineJudges/lydsy/2659.cpp b/OnlineJudges/lydsy/2659.cpp
new file mode 100644
index 0000000..c5d0f99
--- /dev/null
+++ b/OnlineJudges/lydsy/2659.cpp
@@ -0,0 +1,9 @@
+//http://www.cnblogs.com/iwtwiioi/p/4985747.html
+#include <cstdio>
+int main()
+{
+    int p, q;
+    scanf("%d%d", &p, &q);
+    printf("%lld", 1ll * (q - 1) * (p - 1) / 4 + (p == q) * (q - 1) / 2);
+    return 0;
+}
\ No newline at end of file