#include <stdio.h>
#include <map>
#include <set>
#include <vector>
#include <queue>
#include <algorithm>
#define LL long long
#define pii pair<int, int>
#define ff first
#define ss second
#define INF (int)1e9
using namespace std;
vector<int> X, Y;
priority_queue<LL> pq;
struct Indexed_Tree{
int bias;
vector<pii> tree;
void init(int n){
for(bias = 1; bias < n; bias <<= 1);
tree.resize(bias<<1);
for(int i = 0; i < n; i++) tree[i|bias] = {Y[i+1], i};
for(int i = n; i < bias; i++) tree[i|bias] = {INF, INF};
for(int i = bias-1; i; i--) tree[i] = min(tree[i<<1], tree[i<<1|1]);
}
pii query_min(int s, int e){
pii mn = {INF, INF};
s |= bias; e |= bias;
while(s <= e){
if(s&1) mn = min(mn, tree[s++]);
if(~e&1) mn = min(mn, tree[e--]);
s >>= 1; e >>= 1;
}
return mn;
}
}IDT;
LL dfs(int s, int e, int y){
if(s == e) return 0;
//printf("%d %d %d\n", s, e, y);
pii mn = IDT.query_min(s, e-1);
//printf("%d %d\n", mn.ff, mn.ss);
LL res1 = dfs(s, mn.ss, mn.ff);
LL res2 = dfs(mn.ss+1, e, mn.ff);
pq.push(min(res1, res2));
return max(res1, res2)+(X[e]-X[s])*(mn.ff-y);
}
int main(){
int n, k;
scanf("%d", &n);
for(int i = 1; i <= n; i++){
int x, y; scanf("%d %d", &x, &y);
X.push_back(x);
Y.push_back(y);
}
scanf("%d", &k);
X.erase(unique(X.begin(), X.end()), X.end());
Y.erase(unique(Y.begin(), Y.end()), Y.end());
//for(int x : X) printf("%d ", x); printf("\n");
//for(int y : Y) printf("%d ", y); printf("\n");
IDT.init(X.size()-1);
//for(int i = 1; i < (IDT.bias<<1); i++) printf("%d : %d %d\n", i, IDT.tree[i].ff, IDT.tree[i].ss);
pq.push(dfs(0, X.size()-1, 0));
LL sum = 0;
for(;!pq.empty() && k--; pq.pop()) sum += pq.top();
printf("%lld", sum);
return 0;
}
