#include<bits/stdc++.h>
using namespace std;
#define int long long
#define pii pair<int,int>
#define all(x) x.begin(),x.end()
#define pb emplace_back
#define N 100010
#define ff first
#define ss second
pii a[N];
int n,m,ans,c[N];
bool f(int x){
int i,j,mx=0;
priority_queue<int,vector<int>,greater<int>>pq;
for(i=m-x,j=0;i<m;i++){
while(j<n&&a[j].ff<=c[i]) pq.push(a[j++].ss);
while(!pq.empty()&&pq.top()<mx) pq.pop();
if(pq.empty()) return 0;
mx=pq.top(),pq.pop();
}
return 1;
}
signed main(){
ios::sync_with_stdio(0);
cin.tie(0);
int i,j;
cin>>n>>m;
for(i=0;i<n;i++) cin>>a[i].ff>>a[i].ss;
for(i=0;i<m;i++)cin>>c[i];
sort(c,c+m);
sort(a,a+n);
for(i=m,j=0;i;i>>=1){
while(i+j<=m&&f(i+j))
ans=max(ans,i+j),j+=i;
}
cout<<ans<<'\n';
}
