#include <bits/stdc++.h>
using namespace std;
using ll = long long;
#define pb emplace_back
#define AI(i) begin(i), end(i)
template<class T> bool chmin(T &a, T b) { return b < a && (a = b, true); }
template<class T> bool chmax(T &a, T b) { return a < b && (a = b, true); }
#ifdef KEV
#define DE(args...) kout("[ " + string(#args) + " ] = ", args)
void kout() { cerr << endl; }
template<class T, class ...U> void kout(T a, U ...b) { cerr << a << ' ', kout(b...); }
template<class T> void debug(T L, T R) { while (L != R) cerr << *L << " \n"[next(L) == R], ++L; }
#else
#define DE(...) 0
#define debug(...) 0
#endif
const int MAX_N = 300010;
#pragma GCC optimize("Ofast")
int a[MAX_N][2], t[MAX_N], n, m;
int32_t main() {
cin.tie(0)->sync_with_stdio(0);
cin >> n >> m;
for (int i = 0;i < n;++i)
cin >> a[i][0] >> a[i][1];
for (int i = 0;i < m;++i)
cin >> t[i];
ll sum = 0;
for (int i = 0;i < n;++i) {
int c = 0;
for (int j = 0;j < m;++j)
if (a[i][c] <= t[j]) c ^= 1;
sum += a[i][c];
}
cout << sum << '\n';
}
