diff --git a/Makefile b/Makefile
index a225d93..c8d03b7 100644
--- a/Makefile
+++ b/Makefile
@@ -1,4 +1,4 @@
-VERSION := 9.0.3
+VERSION := 9.1.0
 MAJOR_VERSION := $(shell echo $(VERSION) | head -c 1)
 
 # installation directory (/usr/local by default)
diff --git a/src/cs50.c b/src/cs50.c
index 5feac60..a51eec1 100644
--- a/src/cs50.c
+++ b/src/cs50.c
@@ -397,6 +397,43 @@ long get_long(const char *format, ...)
     }
 }
 
+/**
+ * Prompts user for a line of text from standard input and returns the
+ * equivalent long long; if text does not represent a long long in
+ * [-2^63, 2^63 - 1) or would cause underflow or overflow, user is
+ * prompted to retry. If line can't be read, returns LLONG_MAX.
+ */
+long long get_long_long(const string format, ...)
+{
+    va_list ap;
+    va_start(ap, format);
+
+    // Try to get a long long from user
+    while (true)
+    {
+        // Get line of text, returning LLONG_MAX on failure
+        string line = get_string(&ap, format);
+        if (line == NULL)
+        {
+            va_end(ap);
+            return LLONG_MAX;
+        }
+
+        // Return a long long if only a long long (in range) was provided
+        if (strlen(line) > 0 && !isspace((unsigned char) line[0]))
+        {
+            char *tail;
+            errno = 0;
+            long long n = strtoll(line, &tail, 10);
+            if (errno == 0 && *tail == '\0' && n < LLONG_MAX)
+            {
+                va_end(ap);
+                return n;
+            }
+        }
+    }
+}
+
 /**
  * Called automatically after execution exits main.
  */
diff --git a/src/cs50.h b/src/cs50.h
index 2b9d18b..b284ba2 100644
--- a/src/cs50.h
+++ b/src/cs50.h
@@ -94,6 +94,14 @@ int get_int(const char *format, ...) __attribute__((format(printf, 1, 2)));
  */
 long get_long(const char *format, ...) __attribute__((format(printf, 1, 2)));
 
+/**
+ * Prompts user for a line of text from standard input and returns the
+ * equivalent long long; if text does not represent a long long in
+ * [-2^63, 2^63 - 1) or would cause underflow or overflow, user is
+ * prompted to retry. If line can't be read, returns LLONG_MAX.
+ */
+long long get_long_long(const string format, ...) __attribute__((format(printf, 1, 2)));
+
 /**
  * Prompts user for a line of text from standard input and returns
  * it as a string (char *), sans trailing line ending. Supports