Problem:
Score : 200 points

Problem Statement

You are given nonnegative integers a and b (a ≤ b), and a positive integer x.
Among the integers between a and b, inclusive, how many are divisible by x?

Constraints

0 ≤ a ≤ b ≤ 10^{18}

1 ≤ x ≤ 10^{18}

Input

The input is given from Standard Input in the following format:

a b x

Output

Print the number of the integers between a and b, inclusive, that are divisible by x.

Sample Input 1

4 8 2

Sample Output 1

3

There are three integers between 4 and 8, inclusive, that are divisible by 2: 4, 6 and 8.

Sample Input 2

0 5 1

Sample Output 2

6

There are six integers between 0 and 5, inclusive, that are divisible by 1: 0, 1, 2, 3, 4 and 5.

Sample Input 3

9 9 2

Sample Output 3

0

There are no integer between 9 and 9, inclusive, that is divisible by 2.

Sample Input 4

1 1000000000000000000 3

Sample Output 4

333333333333333333

Watch out for integer overflows.

Solution in C (GCC 5.4.1) (judge verdict: Wrong Answer)

#include<stdio.h>
#include<stdlib.h>
#include<string.h>


int main(){
	unsigned long a;
	unsigned long b;
	unsigned long x;

	unsigned long s;
	unsigned long t;
	unsigned long u;

	scanf("%ld",&a);
	scanf("%ld",&b);
	scanf("%ld",&x);

	// printf("a = %ld,b = %ld,x = %ld\n",a,b,x);

	/*for(int i=a;i<=b;i++){
		if(i%x == 0){
			count++;
		}
	}*/

	s = (a-1) / x;
	t = b / x;
	u = t - s;
	if(u <= 0){
		u =0;
	}

	// printf("s = %ld,t = %ld,u = %ld\n",s,t,u);
 
	printf("%ld\n",u);

	return 0;
}