/**
* @brief Codeforces Round #284 (Div. 2) a
* @file a.cpp
* @author mianma
* @created 2014/12/26 11:51
* @edited 2014/12/18 11:51
* @type brute
* @note
*/
#include <fstream>
#include <iostream>
#include <cstring>
using namespace std;
#define max(a, b) ((a) > (b) ? (a) : (b))
#define min(a, b) ((a) > (b) ? (b) : (a))
#define abs(a) ((a) > 0 ? (a) : (0 - (a)))
#define CLR(vec) memset(vec, 0, sizeof(vec))
#ifdef DEBUG
ifstream in;
ofstream out;
#define CIN in
#define COUT out
#else
#define CIN cin
#define COUT cout
#endif
#define MAXN 50
#define MAXV 1e5
int n, x;
int curr, ans, lft, rht;
int main(void){
ios_base::sync_with_stdio(0);
#ifdef DEBUG
CIN.open("./in", ios::in);
COUT.open("./out", ios::out);
#endif
CIN >> n >> x;
int curr = 1;
int ans = 0;
for(int i = 0; i < n; i++){
CIN >> lft >> rht;
if(curr > lft)
lft = curr;
ans += (lft - curr)%x + rht - lft + 1;
curr = rht + 1;
}
COUT << ans << "\n";
return 0;
}
Codeforces Round #284 (Div. 2) a
原文：http://my.oschina.net/u/572632/blog/360810