diff --git a/Luogu/P1503/P1503.cpp b/Luogu/P1503/P1503.cpp
new file mode 100644
index 00000000..0e3dbeb7
--- /dev/null
+++ b/Luogu/P1503/P1503.cpp
@@ -0,0 +1,35 @@
+#include <iostream>
+#include <set>
+#include <stack>
+
+using std::cin;
+using std::cout;
+const char endl = '\n';
+
+int n, m, x;
+char op;
+std::set<int> set;
+std::stack<int> st;
+
+int main() {
+    std::ios::sync_with_stdio(false);
+    cin >> n >> m;
+    set.insert(0);
+    set.insert(n + 1);
+    while (m--) {
+        cin >> op;
+        if (op == 'D') {
+            cin >> x;
+            set.insert(x);
+            st.push(x);
+        } else if (op == 'R') {
+            set.erase(st.top());
+            st.pop();
+        } else {
+            cin >> x;
+            auto it = set.lower_bound(x);
+            cout << (*it == x ? 0 : *it - *--it - 1) << endl;
+        }
+    }
+    return 0;
+}