WA on #3

#include<bits/stdc++.h>
using namespace std;
int const maxn=2.5e5+5;
int n,t,cnt;
pair<int,int>a[maxn];
signed main()
{   
    scanf("%d%d",&n,&t);
    for(int i=1;i<=n;i++)
        scanf("%d%d",&a[i].first,&a[i].second);
    sort(a+1,a+n+1);
    int end=1,j=1;
    while(j<=n)
    {
        int r=0;
        while(j<=n&&a[j].first<=end)
        {
            r=max(r,a[j].second);
            j++;
        }
        cnt++;
        if(r<end)
        {
            printf("-1");
            return 0;
        }
        if(r>=t)
        { 
            printf("%d",cnt);
            return 0;
        }
        end=r+1;
    }
    return 0;
}