#include <bits/stdc++.h>
using namespace std;
using ll = long long;
int main() {
ios::sync_with_stdio(0);
cin.tie(0);
int n;
cin >> n;
vector<int> a(n), b(n);
for (int i = 0; i < n; ++i) {
cin >> a[i] >> b[i];
}
stack<pair<int, int>> right, left;
for (int i = n - 1; i >= 0; --i) {
if (a[i] > 0) right.push({a[i], i});
}
ll res = 0;
for (int i = 0; i < n; ++i) {
while (right.size() && right.top().second < i) {
left.push(right.top());
right.pop();
}
while (b[i] > 0) {
int mn = INT_MAX;
if (right.size()) {
mn = min(mn, abs(i - right.top().second));
}
if (left.size()) {
mn = min(mn, abs(i - left.top().second));
}
if (right.size() && mn == abs(i - right.top().second)) {
int need = min(b[i], right.top().first);
b[i] -= need;
right.top().first -= need;
res += 1LL * need * abs(i - right.top().second);
} else {
int need = min(b[i], left.top().first);
b[i] -= need;
left.top().first -= need;
res += 1LL * need * abs(i - left.top().second);
}
while (left.size() && left.top().first == 0) {
left.pop();
}
while (right.size() && right.top().first == 0) {
right.pop();
}
}
}
cout << res << endl;
}
