#include <bits/stdc++.h>
using namespace std;
 
int n, start;
 
int main() {
	cin>>n;
	n *= 2;
	vector<int> starts;
	starts.push_back(0);
	for(int i = 0; i < 3; i++){
		int a, b;
		cin>>a>>b;
		a *= 2, b *= 2;
		for(int start : starts){
			if(a < start)	a = 2*start - a;
			if(b < start)	b = 2*start - b;
		}
		if(a != b){
			n = max(n, (a+b)-starts.back());
			starts.push_back((a+b)/2);
		}
	}
	printf("%.1f", 0.5*(n-starts.back()));
	return 0;
}

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MTAKMiA3CjUgNAoxMCAz

10
2 7
5 4
10 3