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>
int main()
{
    long int a,b,x,i,count,p;
    while(scanf("%ld %ld %ld", &a,&b,&x)==3)
        if(a<=b && a>=0 && a<=1000000000000000000 && b>=0 && b<=1000000000000000000 && x>=1 && x<=1000000000000000000)
        {
            count=0;
            for(i=a; i<=b; i++)
            {
                if(a==0 && b==0)
                {
                    printf("0\n");
                }
                else
                {
                    if(i%2==0)
                    {
                        count++;
                    }
                    p=1;
                }
            }
            if(p==1)
            {
                printf("%ld\n", count);
            }
        }
        else
        {

        }
    return 0;
}