diff --git a/bjtu/1990/1990.cpp b/bjtu/1990/1990.cpp
new file mode 100644
index 00000000..f3851603
--- /dev/null
+++ b/bjtu/1990/1990.cpp
@@ -0,0 +1,38 @@
+#include <iostream>
+
+using std::cin;
+using std::cout;
+const char endl = '\n';
+
+const int N = 2e5 + 5;
+
+int n, a[N], b[N], s1[N], s2[N], ans;
+
+int main() {
+    std::ios::sync_with_stdio(false);
+    cin.tie(nullptr);
+
+    cin >> n;
+
+    for (int i = 1; i <= n; i++) {
+        cin >> a[i];
+    }
+
+    for (int i = 1; i <= n; i++) {
+        cin >> b[i];
+    }
+
+    for (int i = 1; i <= n; i++) {
+        s1[i] = s1[i - 1] + (a[i] == b[i]);
+        s2[i] = s2[i - 1] + (a[i] == b[i - 1]);
+    }
+
+    ans = s2[n];
+    for (int i = 1; i <= n; i++) {
+        ans = std::max(ans, s1[i - 1] + s2[n] - s2[i] + (a[i] == b[n]));
+    }
+
+    cout << ans << endl;
+
+    return 0;
+}