diff --git a/.github/workflows/verify.yml b/.github/workflows/verify.yml
index 98e13e0..199f5ce 100644
--- a/.github/workflows/verify.yml
+++ b/.github/workflows/verify.yml
@@ -29,6 +29,7 @@ jobs:
         path: |
           .verify-helper/cache/
           ~/.cache/online-judge-tools/library-checker-problems/
+          ~/.local/share/online-judge-tools/
         key: cache-judge-data
 
     - name: Run tests
diff --git a/src/math/FastGCD.hpp b/src/math/FastGCD.hpp
new file mode 100644
index 0000000..63953ef
--- /dev/null
+++ b/src/math/FastGCD.hpp
@@ -0,0 +1,11 @@
+u64 ctz(u64 x) { return countr_zero(x); }
+u64 binary_gcd(u64 x, u64 y) {
+   if(!x || !y) return x | y;
+   u64 n = ctz(x), m = ctz(y);
+   x >>= n, y >>= m;
+   while(x != y) {
+      if(x > y) x = (x - y) >> ctz(x - y);
+      else y = (y - x) >> ctz(y - x);
+   }
+   return x << min(n, m);
+}
diff --git a/test/math/FastGCD.test.cpp b/test/math/FastGCD.test.cpp
new file mode 100644
index 0000000..a9fc9f1
--- /dev/null
+++ b/test/math/FastGCD.test.cpp
@@ -0,0 +1,13 @@
+#define PROBLEM "https://judge.u-aizu.ac.jp/onlinejudge/description.jsp?id=ITP1_1_A"
+#include "test/template.hpp"
+using u64 = uint64_t;
+#include "src/math/FastGCD.hpp"
+
+int main() {
+   mt19937_64 rnd;
+   rep(i, 0, (ll)1e7) {
+      u64 a = rnd(), b = rnd();
+      assert(gcd(a, b) == binary_gcd(a, b));
+   }
+   puts("Hello World");
+}
diff --git a/test/template.test.cpp b/test/template.test.cpp
index fff0ab8..e19b30e 100644
--- a/test/template.test.cpp
+++ b/test/template.test.cpp
@@ -7,5 +7,5 @@ int main() {
     assert(chmax(a, 1) == 1);
     assert(chmax(a, 1) == 0);
     assert(chmin(a, 0) == 1);
-    cout << "Hello World" << endl;
+    puts("Hello World");
 }