diff --git a/RPi/i2c_challenge.c b/RPi/i2c_challenge.c
index 381103d..6b92a05 100644
--- a/RPi/i2c_challenge.c
+++ b/RPi/i2c_challenge.c
@@ -21,20 +21,43 @@
 #include <wiringPi.h>
 #include <wiringPiI2C.h>
 
-#define I2C_ADDR 0x20
-
 uint8_t solve_challenge(uint8_t arg) {
   return (arg >> 3) ^ (arg << 3);
 }
 
+uint8_t parse_int(const char *s) { // Convert string to hex
+  uint8_t result = 0;
+  int c;
+  if ('0' == *s && 'x' == *(s + 1)) {
+    s += 2;
+    while (*s) {
+      result = result << 4;
+      if (c = (*s - '0'), (c >= 0 && c <= 9)) result |= c;
+      else if (c = (*s - 'A'), (c >= 0 && c <= 5)) result |= (c + 10);
+      else if (c = (*s - 'a'), (c >= 0 && c <= 5)) result |= (c + 10);
+      else break;
+      ++s;
+    }
+  }
+  return result;
+}
+
 int main(int argc, char *argv[]) {
 
   int fd; // Linux filehandle to the i2c device
   uint8_t challenge;
   uint8_t response;
+  uint8_t i2c_addr;
+
+  if (argc != 2) {
+    printf("Usage: \n\ti2c_challenge <i2caddr>");
+    return 1;
+  }
+  i2c_addr = parse_int(argv[1]);
+
   wiringPiSetup();
 
-  fd = wiringPiI2CSetup(I2C_ADDR); // Initialize the i2c protocol with the address
+  fd = wiringPiI2CSetup(i2c_addr); // Initialize the i2c protocol with the address
   if (fd == -1) { // Failed to contact device
     printf("Can't setup the I2C device\n");
     return -1;