//寻找l大于i距离i最近的点r
#include <iostream>
#include <algorithm>
#include <queue>

#define l first
#define r second

using namespace std;

const int N = 2e5+10;

typedef pair<int,int>PII;

PII p[N];

int main()
{
    int n,m;
    cin>>n>>m;
    for(int i=1;i<=n;i++) cin>>p[i].l>>p[i].r;
    sort(p+1,p+1+n);
    priority_queue<int,vector<int>,greater<int>>q;
    long long ans=0;
    q.push(m+1);
    for(int i=m,j=n;i>=1;i--)
    {
        while(j>=1&&p[j].l>=i)
        {
            q.push(p[j].r);
            j--;
        }
        ans+=q.top()-i;
    }
    cout<<ans;
    return 0;
}