#include <stdio.h>#define MAX_N 50032#define MAX_R 100032 struct { int a, b;} dp[MAX_N], fences[MAX_N];int N, S, tree[MAX_R*16];__inline int max(int a, int b){ return a > b ? a : b;}__inline int abs(int a){ return a > 0 ? a : -a;}__inline int min(int a, int b){ return a < b ? a : b;}void insert(int idx, int start, int end, int left, int right, int val){ int mid; if (start == left && right == end) { tree[idx] = val; return ; } mid = (start + end) / 2; if (right <= mid) insert(idx*2, start, mid, left, right, val); else if (left > mid) insert(idx*2+1, mid + 1, end, left, right, val); else { insert(idx*2, start, mid, left, mid, val); insert(idx*2+1, mid + 1, end, mid + 1, right, val); }}int query(int idx, int start, int end, int pos){ int val, mid; if (start == pos && end == pos) return tree[idx]; mid = (start + end) / 2; if (pos <= mid) val = query(idx*2, start, mid, pos); else val = query(idx*2+1, mid + 1, end, pos); return max(val, tree[idx]);}__inline int calc_min(int i, int pos){ if (!i) return abs(pos - MAX_R); return min(pos - fences[i].a + dp[i].a, fences[i].b - pos + dp[i].b);}int main(){ int i; scanf("%d%d", &N, &S); S += MAX_R; for (i = 1; i <= N; i++) { scanf("%d%d", &fences[i].a, &fences[i].b); fences[i].a += MAX_R; fences[i].b += MAX_R; dp[i].a = calc_min(query(1, 0, MAX_R*2, fences[i].a), fences[i].a); dp[i].b = calc_min(query(1, 0, MAX_R*2, fences[i].b), fences[i].b); insert(1, 0, MAX_R*2, fences[i].a, fences[i].b, i); } printf( "%dn", min(S - fences[N].a + dp[N].a, fences[N].b - S + dp[N].b) ); return 0;}
