$18.$ A programmer works with an unknown program language. The language provides four$$ different unsigned integer data types with the following storage abilities:$$

int$1$ uses $8$ bits$$

int$2$ uses $16$ bits$$

int$3$ uses $24$ bits$$

int$4$ uses $32$ bits$$

int$5$ uses $64$ bits$$

An unsigned integer uses every bit in the sequence for storage. There is no bit used to indicate a positive or negative number. The int$1$ data type has space for $256$ unique integers in the $[0..255]$ range. This data type is considered inadequate for the needs of the program. Integers need to store numbers as large as $10,000,000.$ Which of the following integer data types uses the least memory, but is adequate for the storage requirement?$$

int$5$

int$2$

int $4$

Int$3$

A is the correct answer because