#include<bits/stdc++.h>
using namespace std;
int n, l[20010], r[20010], f[20010][3];
int dfs(int x, int z) {
    if (x == 1)
        f[x][z] = z ? r[x] : l[x];
    if (f[x][z])
        return f[x][z];
    f[x][z] = 1000000000;
    for (int last = 0; last <= 1; ++last) {
        dfs(x - 1, last);
        f[x][z] = min(f[x][z], abs((z ? r[x] : l[x]) - (last ? r[x - 1] : l[x - 1]) + r[x] - l[x] + 1) + 1 + f[x - 1][last]); 
    }
    //cout << "I'm here! " << x << " " << f[x][z] << "\n"; 
    return f[x][z];
}
int main() {
    ios::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
    cin >> n;
    for (int i = 1; i <= n; ++i) {
        cin >> l[i] >> r[i];
    }
    cout << min(dfs(n, 0) + n - l[n], dfs(n, 1) + n - r[n]); 

    return 0;
}

不胜感激。祝您rp++。