diff --git a/atcoder/abc055/A/main.cpp b/atcoder/abc055/A/main.cpp
new file mode 100644
index 00000000..37dbf5a9
--- /dev/null
+++ b/atcoder/abc055/A/main.cpp
@@ -0,0 +1,17 @@
+#include <bits/stdc++.h>
+
+using namespace std;
+using ll = long long;
+
+int main() {
+    ios_base::sync_with_stdio(false);
+    cin.tie(0); cout.tie(0);
+
+    int N;
+    cin >> N;
+    int x = N * 800;
+    int y = N / 15 * 200;
+    cout << x - y << endl;
+
+    return 0;
+}
\ No newline at end of file
diff --git a/atcoder/abc055/B/main.cpp b/atcoder/abc055/B/main.cpp
new file mode 100644
index 00000000..f9b320ed
--- /dev/null
+++ b/atcoder/abc055/B/main.cpp
@@ -0,0 +1,25 @@
+#include <bits/stdc++.h>
+
+using namespace std;
+using ll = long long;
+
+ll solve(int N) {
+    const ll MOD = 1e9+7;
+    ll p = 1;
+    for (int i = 0; i < N; ++i) {
+        p *= (i+1);
+        p %= MOD;
+    }
+    return p;
+}
+
+int main() {
+    ios_base::sync_with_stdio(false);
+    cin.tie(0); cout.tie(0);
+
+    int N;
+    cin >> N;
+    cout << solve(N) << endl;
+
+    return 0;
+}
\ No newline at end of file
diff --git a/atcoder/abc055/C/main.cpp b/atcoder/abc055/C/main.cpp
new file mode 100644
index 00000000..8ebb5a1e
--- /dev/null
+++ b/atcoder/abc055/C/main.cpp
@@ -0,0 +1,22 @@
+#include <bits/stdc++.h>
+
+using namespace std;
+using ll = long long;
+
+ll solve(ll N, ll M) {
+    if (N >= M / 2) {
+        return M / 2;
+    }
+    return N + (M - 2 * N) / 4;
+}
+
+int main() {
+    ios_base::sync_with_stdio(false);
+    cin.tie(0); cout.tie(0);
+
+    ll N, M;
+    cin >> N >> M;
+    cout << solve(N, M) << endl;
+
+    return 0;
+}
\ No newline at end of file
diff --git a/atcoder/abc055/D/main.cpp b/atcoder/abc055/D/main.cpp
new file mode 100644
index 00000000..d1c76136
--- /dev/null
+++ b/atcoder/abc055/D/main.cpp
@@ -0,0 +1,56 @@
+#include <bits/stdc++.h>
+
+using namespace std;
+using ll = long long;
+
+int N;
+string S;
+
+bool solve(vector<char>& ws, char c0, char c1) {
+    ws[0] = c0, ws[1] = c1;
+    for (int i = 1; i < N; ++i) {
+        int j = (i - 1 + N) % N, k = (i + 1) % N;
+        if (S[i] == 'o') {
+            if (ws[i] == 'S') ws[k] = ws[j];
+            if (ws[i] == 'W') ws[k] = ws[j] == 'S' ? 'W' : 'S';
+        }
+        if(S[i] == 'x') {
+            if (ws[i] == 'S') ws[k] = ws[j] == 'S' ? 'W' : 'S';
+            if (ws[i] == 'W') ws[k] = ws[j];
+        }
+    }
+    bool satisfy = true;
+    for (int i = 0; i < N; ++i) {
+        int j = (i - 1 + N) % N, k = (i + 1) % N;
+        if (S[i] == 'o') {
+            if (ws[i] == 'S') satisfy &= (ws[k] == ws[j]);
+            if (ws[i] == 'W') satisfy &= (ws[k] != ws[j]);
+        }
+        if (S[i] == 'x') {
+            if (ws[i] == 'S') satisfy &= (ws[k] != ws[j]);
+            if (ws[i] == 'W') satisfy &= (ws[k] == ws[j]);
+        }
+    }
+    return satisfy;
+}
+
+vector<char> solve() {
+    vector<char> ws(N, ' ');
+    if (solve(ws, 'S', 'S')) return ws;
+    if (solve(ws, 'S', 'W')) return ws;
+    if (solve(ws, 'W', 'S')) return ws;
+    if (solve(ws, 'W', 'W')) return ws;
+    return {};
+}
+
+int main() {
+    ios_base::sync_with_stdio(false);
+    cin.tie(0); cout.tie(0);
+
+    cin >> N;
+    cin >> S;
+    auto ans = solve();
+    cout << (ans.size() == 0 ? "-1" : string(ans.begin(), ans.end())) << endl;
+
+    return 0;
+}
\ No newline at end of file