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+// Problem: Calculate Alternating Digit Sum
+// Source: https://leetcode.com/problems/alternating-digit-sum/
+// Note: Add and subtract consecutive digits from left to right.
+// Ported from: python/practice101.py
+// Time: O(d), where d is the number of digits.
+
+const readline = require('readline');
+
+const rl = readline.createInterface({
+  input: process.stdin,
+  output: process.stdout
+});
+
+rl.question('Enter a positive integer: ', (input) => {
+  const n = input.trim();
+
+  let plus = true;
+  let res = 0;
+
+  for (const digit of n) {
+    const num = parseInt(digit, 10);
+    res += plus ? num : -num;
+    plus = !plus;
+  }
+
+  console.log(`Sum: ${res}`);
+  rl.close();
+});