#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;
typedef long long ll;
int main() {
int n;
cin >> n;
vector<ll> a(n), b(n);
for (int i = 0; i < n; i++) cin >> a[i] >> b[i];
// L[i] and R[i] represent the feasible corridor for the net flow f_i
vector<ll> L(n + 1, 0), R(n + 1, 0);
// Backward pass: Determine the global constraints needed to reach f_n = 0
// Based on: f_{i-1} must be in [f_i + b_i - a_i, f_i + b_i]
for (int i = n - 1; i >= 0; i--) {
L[i] = L[i + 1] + b[i] - a[i];
R[i] = R[i + 1] + b[i];
}
ll current_f = 0;
ll total_cost = 0;
// Forward pass: Pick the f_i closest to 0 within the feasible corridor
for (int i = 0; i < n; i++) {
// Local range forced by the previous flow:
ll local_L = current_f - b[i];
ll local_R = current_f + a[i] - b[i];
// Intersect with the global corridor [L[i+1], R[i+1]]
ll final_L = max(local_L, L[i + 1]);
ll final_R = min(local_R, R[i + 1]);
// Pick the value in [final_L, final_R] closest to 0
if (0 < final_L) current_f = final_L;
else if (0 > final_R) current_f = final_R;
else current_f = 0;
total_cost += abs(current_f);
}
cout << total_cost << endl;
}
