我已经对着题解检查了一遍又一遍了但是连样例都不对。

#include <iostream>
#include <cmath>
#include <algorithm>
using namespace std;

int n, l[20005], r[20005], dp[20005][2];

int main()
{
    ios::sync_with_stdio(false);
    cin.tie(0);
    cout.tie(0);
    
    cin >> n;
    for (int i = 1; i <= n; i++)
        cin >> l[i] >> r[i];
    dp[1][0] = r[1] + r[1] - l[1] - 1;
    dp[1][1] = r[1] - 1;
    for (int i = 2; i <= n; i++)
    {
        dp[i][0] = min(dp[i - 1][0] + abs(r[i] - l[i - 1]) + r[i] - l[i], dp[i - 1][1] + abs(r[i] - r[i - 1]) + r[i] - l[i]);
        dp[i][1] = min(dp[i - 1][0] + abs(l[i] - l[i - 1]) + r[i] - l[i], dp[i - 1][1] + abs(r[i] - l[i - 1]) + r[i] - l[i]);
    }
    cout << min(dp[n][0] + n - l[n], dp[n][1] + n - r[n]) << "\n";
    return 0;
}