diff --git a/Sources/AtCoderSupport/IntOrDouble.swift b/Sources/AtCoderSupport/IntOrDouble.swift
new file mode 100644
index 0000000..e916a51
--- /dev/null
+++ b/Sources/AtCoderSupport/IntOrDouble.swift
@@ -0,0 +1,56 @@
+struct Iod: CustomStringConvertible, Hashable, Equatable, Comparable, AdditiveArithmetic, ExpressibleByIntegerLiteral {
+    typealias IntegerLiteralType = Int
+    let intValue: Int
+    let doubleValue: Double
+    let isInt: Bool
+    var description: String {
+        isInt ? "\(intValue)(f: \(doubleValue))" : "\(doubleValue)(i: \(intValue))"
+    }
+    init(_ i: Int) {
+        intValue = i
+        doubleValue = Double(i)
+        isInt = true
+    }
+    init(_ d: Double) {
+        intValue = Int(d)
+        doubleValue = d
+        isInt = false
+    }
+    init(integerLiteral value: IntegerLiteralType) {
+        intValue = Int(value)
+        doubleValue = Double(value)
+        isInt = type(of: value) == Int.self
+    }
+
+    static var zero = Iod(0)
+    static func + (lhs: Self, rhs: Self) -> Self { proc(lhs, rhs, +, +) }
+    static func - (lhs: Self, rhs: Self) -> Self { proc(lhs, rhs, -, -)}
+    static func * (lhs: Self, rhs: Self) -> Self { proc(lhs, rhs, *, *) }
+    static func / (lhs: Self, rhs: Self) -> Self { proc(lhs, rhs, /, /) }
+    static func += (lhs: inout Self, rhs: Self) { lhs = lhs + rhs }
+    static func -= (lhs: inout Self, rhs: Self) { lhs = lhs - rhs }
+    static func *= (lhs: inout Self, rhs: Self) { lhs = lhs * rhs }
+    static func /= (lhs: inout Self, rhs: Self) { lhs = lhs / rhs }
+
+    static func < (lhs: Self, rhs: Self) -> Bool {
+        preconditionCheck(note: "compare", lhs: lhs, rhs: rhs)
+        return lhs.isInt ? lhs.intValue < rhs.intValue : lhs.doubleValue < rhs.doubleValue
+    }
+    static func == (lhs: Self, rhs: Self) -> Bool {
+        preconditionCheck(note: "equal", lhs: lhs, rhs: rhs)
+        return lhs.isInt ? lhs.intValue == rhs.intValue : lhs.doubleValue == rhs.doubleValue
+    }
+    private static func proc(_ lhs:Self, _ rhs:Self, _ f:(Int, Int) -> Int, _ g:(Double, Double) -> Double) -> Self {
+        preconditionCheck(lhs: lhs, rhs: rhs)
+        let i = f(lhs.intValue, rhs.intValue)
+        let d = g(lhs.doubleValue, rhs.doubleValue)
+        return lhs.isInt ? Iod(i) : Iod(d)
+    }
+    private static func preconditionCheck(note: String = "", lhs: Self, rhs: Self) {
+        if lhs.isInt != rhs.isInt {
+            let u = lhs.isInt ? "Int" : "Double"
+            let v = rhs.isInt ? "Int" : "Double"
+            fatalError("Cannot perform \(note)! lhs is \(u), rhs is \(v)")
+        }
+    }
+}