diff --git a/2016/day20/Cargo.lock b/2016/day20/Cargo.lock
new file mode 100644
index 0000000..3d9e495
--- /dev/null
+++ b/2016/day20/Cargo.lock
@@ -0,0 +1,4 @@
+[root]
+name = "day20"
+version = "0.1.0"
+
diff --git a/2016/day20/Cargo.toml b/2016/day20/Cargo.toml
new file mode 100644
index 0000000..f017063
--- /dev/null
+++ b/2016/day20/Cargo.toml
@@ -0,0 +1,6 @@
+[package]
+name = "day20"
+version = "0.1.0"
+authors = ["~krowbar"]
+
+[dependencies]
diff --git a/2016/day20/small_data b/2016/day20/small_data
new file mode 100644
index 0000000..cce656e
--- /dev/null
+++ b/2016/day20/small_data
@@ -0,0 +1,4 @@
+5-8
+0-2
+4-7
+6-7
\ No newline at end of file
diff --git a/2016/day20/src/main.rs b/2016/day20/src/main.rs
new file mode 100644
index 0000000..a3a84e2
--- /dev/null
+++ b/2016/day20/src/main.rs
@@ -0,0 +1,78 @@
+use std::io::Read;
+use std::fs::File;
+use std::cmp;
+
+#[derive(Debug, PartialOrd, PartialEq, Eq, Ord)]
+struct Range {
+    low: u32,
+    high: u32,
+}
+
+fn between(low: u32, high: u32) -> u32 {
+    if low >= high {
+        return 0;
+    }
+    high - low - 1
+}
+
+fn process_addresses(file_name: &str, max_addr: u32) -> (u32, u32) {
+    let mut file = File::open(file_name).expect("could not open file");
+    let mut input = String::new();
+    file.read_to_string(&mut input).expect("could not read file");
+    let mut lines = input.lines().map(|l| {
+        let values: Vec<&str> = l.split("-").collect();
+        Range { low: values[0].parse::<u32>().unwrap(), high: values[1].parse::<u32>().unwrap() }
+    }).collect::<Vec<_>>();
+    lines.sort();
+
+    let mut last_high = 0; //since testable range starts at 0
+    let mut first_good = 0;
+    let mut good_count = 0;
+    let first = lines.iter().next().unwrap();
+    println!("{} ->", first.low);
+    'outer: for line in lines.iter() {
+        if last_high > line.high {
+            continue 'outer; //and keep the old last_high
+        }
+        //println!("{:?}", line);
+        if last_high + 2 > line.low {
+            // it is contiguous or within range of the previous range and there are no new good addresses
+            //println!("({} -> {})", last_high, line.high);
+        } else {
+            // there is a gap between las_high and our current low
+            println!("{} ({}) {} -> ", last_high, between(last_high, line.low), line.low);
+            if first_good == 0 {
+                first_good = last_high + 1;
+                //break 'outer;
+            }
+            //count the gap between the last range's high and our current last_high
+            good_count = good_count + between(last_high, line.low);
+            //print!("{} -> ", good_count);
+        }
+        last_high = cmp::max(last_high, line.high)
+    }
+    //let last = lines.iter().last().unwrap();
+    println!("{} ({}) {}", last_high, between(last_high, max_addr), max_addr);
+    if last_high < max_addr {
+        good_count = good_count + between(last_high, max_addr) + 1; //inclusive of highest value
+    }
+    (first_good, good_count)
+}
+
+fn main() {
+    let (first_good, good_count) = process_addresses("./data", 4294967288);
+    println!("Part 1: First nonblocked address is {}", first_good);
+    println!("Part 2: Counted {} valid addresses", good_count);
+}
+
+#[test]
+fn test_between() {
+    assert_eq!(8, between(1,10));
+}
+
+#[test]
+fn small_test() {
+    let (first_good, good_count) = process_addresses("./small_data", 11);
+    assert_eq!(3, first_good);
+    assert_eq!(4, good_count);
+}
\ No newline at end of file