diff --git a/CMakeLists.txt b/CMakeLists.txt
index 14eb77a..5b6db61 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -11,6 +11,7 @@ set(SOURCES
     src/stack.c
     src/binarytree.c
     src/input.c
+    src/math.c
 )
 
 add_library(flint ${SOURCES})
diff --git a/include/input.h b/include/input.h
index 08fed0e..a6d67f6 100644
--- a/include/input.h
+++ b/include/input.h
@@ -4,7 +4,7 @@
 #include <stdlib.h>
 
 char *get_input(const char *);
-char **split(const char *, size_t *, const char *);
+char **split(char *, size_t *, const char *);
 char **get_lines(const char *, size_t *);
 int *get_ints(const char *, size_t *);
 void del_split(char **);
diff --git a/include/math.h b/include/math.h
new file mode 100644
index 0000000..56bf2d4
--- /dev/null
+++ b/include/math.h
@@ -0,0 +1,8 @@
+#ifndef LIBFLINT_H_MATH
+#define LIBFLINT_H_MATH
+
+int max_int(int a, int b);
+int min_int(int a, int b);
+int binstr_to_int(const char *s);
+
+#endif // LIBFLINT_H_MATH
diff --git a/src/input.c b/src/input.c
index ad439fe..f892896 100644
--- a/src/input.c
+++ b/src/input.c
@@ -36,7 +36,7 @@ char *get_input(const char *path) {
     return buf;
 }
 
-char **split(const char *s, size_t *lsz, const char *delim) {
+char **split(char *s, size_t *lsz, const char *delim) {
     char **lines = NULL;
     char *t = strtok(s, delim);
     size_t n = 0;
diff --git a/src/math.c b/src/math.c
new file mode 100644
index 0000000..13a4647
--- /dev/null
+++ b/src/math.c
@@ -0,0 +1,28 @@
+#include <string.h>
+
+#include "math.h"
+
+int max_int(int a, int b) {
+    if (a > b) {
+        return a;
+    }
+    return b;
+}
+
+int min_int(int a, int b) {
+    if (a < b) {
+        return a;
+    }
+    return b;
+}
+
+int binstr_to_int(const char *s) {
+    int n = 0, m = 1;
+    for (size_t i = strlen(s) - 1; i >= 0; --i) {
+        if (s[i] == '1') {
+            n += m;
+        }
+        m *= 2;
+    }
+    return n;
+}