#include <iostream>

using namespace std;
const int N = (1<<20) + 1;
int Mx[N<<1];

void insert(int i,int val,int cur = 1,int st = 1,int en = N){
	if (i >= en or i < st)
		return;
	if (en - st == 1){
		Mx[cur] = val;
		return;
	}

	int lc = cur + cur,rc = lc + 1,mid = (st + en) / 2;
	insert(i,val,lc,st,mid);
	insert(i,val,rc,mid,en);

	Mx[cur] = max(Mx[lc],Mx[rc]);
}

int get(int l,int r,int cur = 1,int st = 1,int en = N){
	if (l >= en or r <= st)
		return 0;
	if (l <= st and r >= en)
		return Mx[cur];
	int lc = cur + cur,rc = lc + 1,mid = (st + en) / 2;
	return max(get(l,r,lc,st,mid),get(l,r,rc,mid,en));
}

int main(){
	int c,p;
	cin>>c>>p;

	for (int i=1,m,s;i<=c;i++){
		cin>>m>>s;
		insert(m,s);
	}

	long long ans = 0;

	for (int i=1,q,d;i<=p;i++){
		cin>>q>>d;
		ans += max(0,get(1,q+1) - d);
	}

	cout<<ans<<'\n';
}