1 files changed, 27 insertions, 0 deletions
diff --git a/2020/day18.c b/2020/day18.c
new file mode 100644
index 0000000..337f107
--- /dev/null
+++ b/2020/day18.c
@@ -0,0 +1,27 @@
+#include <stdio.h>
+#include <stdlib.h>
+static long parse(void) {
+	long result = 0;
+	char op = '+';
+	for (char ch; EOF != (ch = getchar());) {
+		long val = 0;
+		switch (ch) {
+			break; case ' ': continue;
+			break; case '(': val = parse();
+			break; case ')': return result;
+			break; case '\n': return result;
+			break; case '0' ... '9': val = ch - '0';
+			break; default: op = ch; continue;
+		}
+		switch (op) {
+			break; case '+': result += val;
+			break; case '*': result *= val;
+		}
+	}
+	return result;
+}
+int main(void) {
+	long sum = 0;
+	for (long line; (line = parse()); sum += line);
+	printf("%ld\n", sum);
+}