diff --git a/.github/workflows/python-package.yml b/.github/workflows/python-package.yml
index a956e73..f37e711 100644
--- a/.github/workflows/python-package.yml
+++ b/.github/workflows/python-package.yml
@@ -5,37 +5,36 @@ name: Python package
 
 on:
   push:
-    branches: [ master ]
+    branches: [master]
   pull_request:
-    branches: [ master ]
+    branches: [master]
 
 jobs:
   build:
-
     runs-on: ubuntu-latest
     strategy:
       matrix:
         python-version: [3.6, 3.7, 3.8]
 
     steps:
-    - uses: actions/checkout@v2
-    - name: Set up Python ${{ matrix.python-version }}
-      uses: actions/setup-python@v2
-      with:
-        python-version: ${{ matrix.python-version }}
-    - name: Install dependencies
-      run: |
-        python -m pip install --upgrade pip
-        pip install .[lint,test]
-    - name: Lint with flake8
-      run: |
-        # stop the build if there are Python syntax errors or undefined names
-        flake8 . --count --select=E9,F63,F7,F82 --show-source --statistics
-        # exit-zero treats all errors as warnings. The GitHub editor is 127 chars wide
-        flake8 . --count --exit-zero --max-complexity=10 --max-line-length=127 --statistics
-    - name: Type check with mypy
-      run: |
-        mypy .
-    - name: Test with pytest
-      run: |
-        pytest
+      - uses: actions/checkout@v2
+      - name: Set up Python ${{ matrix.python-version }}
+        uses: actions/setup-python@v2
+        with:
+          python-version: ${{ matrix.python-version }}
+      - name: Install dependencies
+        run: |
+          python -m pip install --upgrade pip
+          pip install .[lint,test]
+      - name: Lint with flake8
+        run: |
+          # stop the build if there are Python syntax errors or undefined names
+          flake8 . --count --select=E9,F63,F7,F82 --show-source --statistics
+          # exit-zero treats all errors as warnings. The GitHub editor is 127 chars wide
+          flake8 . --count --exit-zero --max-complexity=10 --max-line-length=127 --statistics
+      - name: Type check with mypy
+        run: |
+          mypy . --exclude example/
+      - name: Test with pytest
+        run: |
+          pytest
diff --git a/atcoder/math.py b/atcoder/math.py
index c50ca88..7ad491f 100644
--- a/atcoder/math.py
+++ b/atcoder/math.py
@@ -16,15 +16,12 @@ def inv_mod(x: int, m: int) -> int:
 def crt(r: typing.List[int], m: typing.List[int]) -> typing.Tuple[int, int]:
     assert len(r) == len(m)
 
-    n = len(r)
-
     # Contracts: 0 <= r0 < m0
     r0 = 0
     m0 = 1
-    for i in range(n):
-        assert 1 <= m[i]
-        r1 = r[i] % m[i]
-        m1 = m[i]
+    for r1, m1 in zip(r, m):
+        assert 1 <= m1
+        r1 %= m1
         if m0 < m1:
             r0, r1 = r1, r0
             m0, m1 = m1, m0