diff --git a/2022/puzzle-25-01.cc b/2022/puzzle-25-01.cc
new file mode 100644
index 0000000..7a075af
--- /dev/null
+++ b/2022/puzzle-25-01.cc
@@ -0,0 +1,114 @@
+//
+// Created by Matthew Gretton-Dann on 16/12/2022.
+//
+
+#include <array>
+#include <iostream>
+#include <stdexcept>
+#include <utility>
+
+using namespace std::string_literals;
+
+using Int = std::int64_t;
+using UInt = std::uint64_t;
+
+auto to_base10(std::string const& s) -> Int
+{
+  Int num{0};
+  for (auto c : s) {
+    num *= 5;
+    switch (c) {
+    case '=':
+      num -= 2;
+      break;
+    case '-':
+      num -= 1;
+      break;
+    case '0':
+      break;
+    case '1':
+      num += 1;
+      break;
+    case '2':
+      num += 2;
+      break;
+    default:
+      abort();
+    }
+  }
+  return num;
+}
+
+auto to_base5(Int num) -> std::string
+{
+  bool const negate{num < 0};
+  if (negate) {
+    num = -num;
+  }
+
+  std::string result;
+  while (num != 0) {
+    Int digit = num % 5;
+    num /= 5;
+    switch (digit) {
+    case 0:
+    case 1:
+    case 2:
+      result.push_back(static_cast<char>('0' + digit));
+      break;
+    case 3:
+      result.push_back('=');
+      num += 1;
+      break;
+    case 4:
+      result.push_back('-');
+      num += 1;
+      break;
+    default:
+      abort();
+    }
+  }
+  std::reverse(result.begin(), result.end());
+
+  if (negate) {
+    for (auto& c : result) {
+      switch (c) {
+      case '=':
+        c = '2';
+        break;
+      case '-':
+        c = '1';
+        break;
+      case '0':
+        c = '0';
+        break;
+      case '1':
+        c = '-';
+        break;
+      case '2':
+        c = '=';
+        break;
+      default:
+        abort();
+      }
+    }
+  }
+
+  return result;
+}
+
+auto main() -> int
+{
+  std::string line;
+  Int total{0};
+
+  while (std::getline(std::cin, line)) {
+    Int const base10{to_base10(line)};
+    total += base10;
+    std::cout << line << " = " << base10 << "\n";
+  }
+
+  std::string const base5{to_base5(total)};
+  std::cout << "Total: " << total << " = " << base5 << "\n";
+  return EXIT_SUCCESS;
+}