codeforces - 597A

A. Divisibility
time limit per test1 second
memory limit per test256 megabytes
inputstandard input
outputstandard output
Find the number of k-divisible numbers on the segment [a, b]. In other words you need to find the number of such integer values x that a ≤ x ≤ b and x is divisible by k.

Input
The only line contains three space-separated integers k, a and b (1 ≤ k ≤ 1018; - 1018 ≤ a ≤ b ≤ 1018).

Output
Print the required number.

Examples
input
1 1 10
output
10
input
2 -4 4
output
5
题解：本题按一般方法会超时，主要考数学知识方法如下
a / b = n 则 n 就代表是1~a范围内可以整除b的个数；

#include <stdio.h>int main(){    long long k, a, b;    long long ans;    while(scanf("%lld%lld%lld", &k, &a, &b) != EOF)    {        if(a <= 0 && b <= 0)          {              __int64 t = a;            a = b;             b = t;              a = -a; b = -b;          }          if(a <= 0 && b >= 0)          {              a = -a;              ans = 1 + b / k + a / k;          }          else              ans = b / k - (a-1) / k;          printf("%lld\n", ans);    }    return 0;}