Wrong Answer.wrong answer On line 1 column 1, read 4, expected 1.

#include<bits/stdc++.h>
using namespace std;
int main(){	
	int n;
	cin >> n;
	int dp[20005],l[20005],r[20005],dp1[20005];
	for(int i=1;i<=n;i++){
		cin >> l[i] >> r[i];
	}
	for(int i=1;i<=n;i++){
		dp1[i]=i-2;
	}
//	for(int i=r[1]-1;i>=1;i--){
//		dp1[i]=dp1[i+1]+1;
//	}
//	for(int k=1;k<=n;k++){
//		cout << dp1[k] << " ";
//	}
//	cout << endl;
	for(int i=1;i<=n;i++){
		int len=abs(r[i]-l[i]);
		for(int j=l[i];j<=r[i];j++){
			dp[j]=min(dp1[r[i]]+1+len+j-l[i],dp1[l[i]]+1+len+r[i]-j);
		}
		for(int j=l[i]-1;j>=0;j--){
			dp[j]=dp[j+1]+1;
		}
		for(int j=r[i]+1;j<=n+1;j++){
			dp[j]=dp[j-1]+1;
		}
//		for(int k=1;k<=n;k++){
//			cout << dp[k] << " ";
//		}
//		cout << endl;
		for(int j=1;j<=n;j++){
			dp1[j]=dp[j];
		}
	}
	cout << dp[n] << endl;
}