diff --git a/Makefile b/Makefile
index c485a24..0973499 100644
--- a/Makefile
+++ b/Makefile
@@ -1,3 +1,10 @@
 default:
-	g++ main.cpp -o collatz
+	cp withgmp.hpp include.hpp
+	g++ -Wall -Wextra -pedantic -Werror -lgmp -lgmpxx main.cpp -o collatz
 	strip collatz
+	rm include.hpp
+gmpless:
+	cp nongmp.hpp include.hpp
+	g++ -Wall -Wextra -pedantic -Werror main.cpp -o collatz
+	strip collatz
+	rm include.hpp
diff --git a/README.md b/README.md
index 3ae914f..4b594c1 100644
--- a/README.md
+++ b/README.md
@@ -1,15 +1,14 @@
 # Collatz conjecture solver
 ### (x%2==0) ? x/=2 : x=x*3+1;
 
-### You probably want the GMP version for arbitrarily big numbers. Get it from the [GMP branch](https://git.sdf.org/ilikecats/collatz/src/branch/gmp).
+Program to solve the [Collatz conjecture](https://en.wikipedia.org/wiki/Collatz_conjecture).
 
-Program to solver the [Collatz conjecture](https://en.wikipedia.org/wiki/Collatz_conjecture).
+To build:
+- With GMP: Run `make -j1` (any more than `-j1` doesn't really do anything, there's four things to do and they can't be put out of order).
+- Without GMP: Run `make gmpless -j1` (see above parenthetical statement).
 
 Algorithm:
 - Start with number.
 - If number is even, divide by two.
 - If number is odd, multiply by three and add one.
 - Repeat.
-
-To figure out if it will repeat, save all the previous numbers, and check if the current number is one of those.
-If it is, that means it will repeat, and you have disproved the Collatz conjecture. So far, though, nobody has disproven it up to 2^68.
diff --git a/main.cpp b/main.cpp
index 712105f..7f86a13 100644
--- a/main.cpp
+++ b/main.cpp
@@ -15,7 +15,7 @@
  */
 
 #include <iostream>
-#include <string>
+#include "include.hpp" // For optional gmpless building (see Makefile)
 
 // TODO:
 //  Make disproving mode
@@ -27,13 +27,26 @@ int main(int argc, char* argv[]) {
     std::cout << "Usage: " << argv[0] << " <number>\n";
     exit(1);
   }
-  long long x { std::stoll(argv[1]) };
-  std::cout << x << '\n';
-  while (x != 1) {
-    if (x % 2 == 0)
-      x /= 2;
-    else if (x % 2)
-      x = x*3+1;
+  mpz_t x; // mpz_t is the GMP equiv. of int
+  mpz_t xmod2; // Store x % 2
+  // Init vars (if not disabled init)
+#ifndef GMPLESS
+  mpz_init_set_str(x, argv[1],10);
+  mpz_init(xmod2);
+#else
+  x = std::stoll(argv[1]);
+#endif
+  // Output x
+  std::cout << x << '\n';                                 // impacted section of code
+  // while x != 1 (mpz_cmp_ui is >0 if x>1, ==0 if x==1, and <0 if x<1, so !=0 means if not equal)
+  while (mpz_cmp_ui(x,1) != 0) {
+    mpz_mod_ui(xmod2,x,2); // xmod2 = x % 2
+    if (mpz_cmp_ui(xmod2,0) == 0) { // If xmod2 == 0
+      mpz_cdiv_q_ui(x,x,2); // x /= 2
+    } else { // If xmod2 != 0
+      mpz_mul_ui(x,x,3); // x *= 3
+      mpz_add_ui(x,x,1); // x += 1
+    }
     std::cout << x << '\n';
   }
 }
diff --git a/nongmp.hpp b/nongmp.hpp
new file mode 100644
index 0000000..e75f283
--- /dev/null
+++ b/nongmp.hpp
@@ -0,0 +1,11 @@
+
+#include <string>
+
+// Make it build gmpless
+#define mpz_t long long
+#define GMPLESS
+#define mpz_cmp_ui(a,b) (a != b)
+#define mpz_mod_ui(a,b,c) a = b % c
+#define mpz_cdiv_q_ui(a,b,c) a = b / c
+#define mpz_mul_ui(a,b,c) a = b * c
+#define mpz_add_ui(a,b,c) a = b + c
diff --git a/withgmp.hpp b/withgmp.hpp
new file mode 100644
index 0000000..6fbb4de
--- /dev/null
+++ b/withgmp.hpp
@@ -0,0 +1 @@
+#include <gmpxx.h>
\ No newline at end of file