#include <iostream>
#include <vector>
#include <set>
#include <algorithm>
using namespace std;
const int N = 1<<17;
int dp[N], strt[N];
int main(){
ios_base::sync_with_stdio(false); cin.tie(NULL); cout.tie(NULL);
int n, m, ans = 0;
cin>>n>>m;
vector<pair<int,int>> vec(n);
vector<int> c(m);
for (int i=0;i<n;i++)
cin>>vec[i].second>>vec[i].first;
sort(begin(vec), end(vec));
for (int i=0;i<m;i++)
cin>>c[i];
sort(begin(c), end(c));
for (int i=1;i<=n;i++)
dp[i] = 2e9;
dp[0] = -1;
vector<int> stt = {0, 1};
strt[0] = strt[1] = 1;
for (auto [b, a] : vec){
int k = upper_bound(begin(c), end(c), a - 1) - begin(c), upd = 0;
int u = upper_bound(dp, dp + n + 1, k) - dp;
// cout<<k<<endl;
vector<int> add;
// cout<<"starts : ";
while (stt.back() >= u and (stt.back() != u or dp[stt.back()] > k + 1)){
if (u == stt.back())
upd = 1;
// cout<<u<<' ';
int id = stt.back();
dp[id] = max(dp[id - 1] + 1, k);
if (dp[id - 1] + 1 >= dp[id])
strt[id] = 0;
if (strt[id + 1] == 0 and dp[id + 1] > dp[id] + 1){
strt[id + 1] = 1;
add.push_back(id + 1);
}
if (strt[id] == 1)
add.push_back(id);
stt.pop_back();
}
// cout<<'\n';
if (dp[u] == k + 1 and upd == 0){
dp[u] = max(k, dp[u-1] + 1);
if (strt[u + 1] == 0 and dp[u] == k and dp[u+1] == k + 2){
strt[u + 1] = 1;
add.push_back(u + 1);
}
if (strt[u] and dp[u - 1] >= k - 1){
stt.pop_back();
strt[u] = 0;
}
}
reverse(begin(add), end(add));
for (int i : add)
stt.push_back(i);
// for (int i=0;i<=n;i++)
// cout<<i<<" "<<strt[i]<<" "<<dp[i]<<endl;
// cout<<endl<<endl<<endl;
}
for (int i=n;i>=0;i--)
if (dp[i] < m)
return cout<<i<<'\n', 0;
}
