diff --git a/in/10.txt b/in/10.txt
new file mode 100644
index 0000000..f7374a0
--- /dev/null
+++ b/in/10.txt
@@ -0,0 +1,95 @@
+76
+12
+97
+28
+132
+107
+145
+121
+84
+34
+115
+127
+22
+23
+11
+135
+113
+82
+140
+119
+69
+77
+83
+36
+13
+37
+92
+133
+122
+99
+147
+112
+42
+62
+65
+40
+123
+139
+33
+129
+149
+68
+41
+16
+48
+109
+5
+27
+142
+81
+90
+9
+78
+103
+26
+100
+141
+59
+55
+120
+126
+1
+35
+2
+20
+114
+58
+54
+10
+51
+116
+93
+6
+134
+108
+47
+70
+91
+138
+63
+19
+64
+148
+106
+21
+98
+43
+30
+146
+46
+128
+73
+94
+87
+29
diff --git a/source/app.d b/source/app.d
index 252b291..bb2fd72 100644
--- a/source/app.d
+++ b/source/app.d
@@ -17,6 +17,7 @@ import day6;
 import day7;
 import day8;
 import day9;
+import day10;
 import dayutil;
 
 immutable string progName = "aoc-2020";
@@ -35,6 +36,7 @@ Variant function(int, File, bool, string[])[] programs = [
 	&day7.run,
 	&day8.run,
 	&day9.run,
+	&day10.run,
 ];
 
 void printUsage(string message = null) {
diff --git a/source/day10.d b/source/day10.d
new file mode 100644
index 0000000..3a5e8a9
--- /dev/null
+++ b/source/day10.d
@@ -0,0 +1,38 @@
+import std.array;
+import std.algorithm;
+import std.conv;
+import std.range;
+import std.stdio;
+import std.variant;
+
+import dayutil;
+
+Variant run(int part, File input, bool bigboy, string[] args) {
+	uint[] numbers = input.byLineCopy.map!(to!uint).array ~ [0u];
+	auto sortedNumbers = numbers.sort;
+
+	Variant result = parts!size_t(part,
+			() => part1(sortedNumbers));
+	return result;
+}
+
+size_t part1(T)(SortedRange!(T[]) numbers) {
+	size_t gap1 = 0, gap3 = 0;
+
+	foreach(window; numbers.slide!(No.withPartial)(2)) {
+		size_t diff = window[1] - window[0];
+		if (diff == 3) gap3++;
+		if (diff == 1) gap1++;
+	}
+	// Device adapter is always rated 3 volts higher
+	gap3++;
+	writeln(gap1, ", ", gap3);
+	return gap1 * gap3;
+}
+
+unittest {
+	uint[] numbers = [28, 33, 18, 42, 31, 14, 46, 20, 48, 47, 24, 23, 49, 45, 19, 38, 39, 11, 1, 32, 
+		 25, 35, 8, 17, 7, 9, 4, 2, 34, 10, 3];
+	numbers ~= [0u];
+	assert(part1(numbers.sort) == 220);
+}