diff --git a/src/0002.concatstring/concat_string.cc b/src/0002.concatstring/concat_string.cc
index 50b0e33..0de9823 100644
--- a/src/0002.concatstring/concat_string.cc
+++ b/src/0002.concatstring/concat_string.cc
@@ -2,43 +2,39 @@
 #include <fast_io.h>
 #include <version>
 
-struct benchmark_return
-{
-	std::size_t total_size{};
-	fast_io::unix_timestamp timestamp{};
+struct benchmark_return {
+  std::size_t total_size{};
+  fast_io::unix_timestamp timestamp{};
 };
 
-template <typename Func>
-inline benchmark_return benchmark(Func meth)
-{
-	std::size_t total_size{};
-	auto start{fast_io::posix_clock_gettime(fast_io::posix_clock_id::monotonic_raw)};
-	for (std::uint_least16_t r{}; r != 256; ++r)
-	{
-		for (std::uint_least16_t g{}; g != 256; ++g)
-		{
-			for (std::uint_least16_t b{}; b != 256; ++b)
-			{
-				total_size += meth(static_cast<::std::uint_least8_t>(r), static_cast<::std::uint_least8_t>(g),
-								   static_cast<::std::uint_least8_t>(b))
-								  .size();
-			}
-		}
-	}
-	return {total_size, fast_io::posix_clock_gettime(fast_io::posix_clock_id::monotonic_raw) - start};
+template <typename Func> inline benchmark_return benchmark(Func meth) {
+  std::size_t total_size{};
+  auto start{
+      fast_io::posix_clock_gettime(fast_io::posix_clock_id::monotonic_raw)};
+  for (std::uint_least16_t r{}; r != 256; ++r) {
+    for (std::uint_least16_t g{}; g != 256; ++g) {
+      for (std::uint_least16_t b{}; b != 256; ++b) {
+        total_size += meth(static_cast<::std::uint_least8_t>(r),
+                           static_cast<::std::uint_least8_t>(g),
+                           static_cast<::std::uint_least8_t>(b))
+                          .size();
+      }
+    }
+  }
+  return {total_size,
+          fast_io::posix_clock_gettime(fast_io::posix_clock_id::monotonic_raw) -
+              start};
 }
 
-inline auto color_concat (std::uint_least8_t r, std::uint_least8_t g, std::uint_least8_t b)
-{
-	return ::fast_io::concat("Red: ", r, ", Green: ", g, ", Blue: ", b);
+inline auto color_concat(std::uint_least8_t r, std::uint_least8_t g,
+                         std::uint_least8_t b) {
+  return ::fast_io::concat_std("Red: ", r, ", Green: ", g, ", Blue: ", b);
 }
 
-
-int main()
-{
-	auto concat_time = benchmark(color_concat);
-	using namespace fast_io::io;
-	print("fast_io::concat (total size: ",
-		concat_time.total_size, ") took ", concat_time.timestamp,
-		"s.\n");
+int main() {
+  auto concat_time = benchmark(color_concat);
+  using namespace fast_io::io;
+  perrln("concat_string:", concat_time.timestamp, "s");
+  print("fast_io::concat_std (total size: ", concat_time.total_size, ") took ",
+        concat_time.timestamp, "s.\n");
 }
diff --git a/src/0006.vector_push_back/vector_push_back.cc b/src/0006.vector_push_back/vector_push_back.cc
index 68d2bb4..d3b52a7 100644
--- a/src/0006.vector_push_back/vector_push_back.cc
+++ b/src/0006.vector_push_back/vector_push_back.cc
@@ -4,7 +4,7 @@
 
 int main()
 {
-	constexpr ::std::size_t N{20000000};
+	constexpr ::std::size_t N{5000000};
 	::std::size_t capacity{};
 	{
 		::fast_io::timer timer_total(u8"::fast_io::vector<::std::size_t>");