58分代码，求大佬看看哪里错了

题目传送

代码如下

#include<bits/stdc++.h>
using namespace std;
struct xianduan
{
	int l;
	int r;
}a[40000];
int main()
{
	int n;
	cin>>n;
	int sum = 0;
	for(int i=1;i<=n;i++)
	{
		cin>>a[i].l;
		cin>>a[i].r;
	}
	int x=1;
	for(int i=1;i<n;i++)
	{
		if(x <= a[i].l)
		{
			sum = sum + (a[i].r - x);
			x = a[i].r;
		}
		else if(x >= a[i].r)
		{
			sum = sum + (x - a[i].l);
			x = a[i].l;
		}
		sum ++;
//		cout<<i<<" "<<x<<endl;
	}
	if(x <= a[n].l)
	{
		sum = sum + (a[n].r - x);
		x = a[n].r;
	}
	else if(x >= a[n].r)
	{
		sum = sum + (x - a[n].l);
		x = a[n].l;
	}
	sum = sum + (n - x);
	cout<<sum;
	return 0;
}