#include <iostream>
#include <stdio.h>
#include <string.h>
#include <map>
#include <set>
#include <vector>
#include <string>
#include <algorithm>
#include <iomanip>

using namespace std;

inline float minOf(float x, float y){return (x<y?x:y);}
inline float maxOf(float x, float y){return (x>y?x:y);}

int main()
{
	ios_base::sync_with_stdio(false);
	int n;
	cin >> n;
	int a[4005];
	string s;
	int pos;
	for(int i =1;i<=2*n;i++){
		cin >> s;
		pos = 0;
		while(s[pos]!= '.')
		pos++;
		pos++;
		a[i] = 0;
		for(int j = 0;j<3;j++)
		a[i] = a[i]*10 + s[pos++]-'0';
	}
	int dp[4005][2005];
	int x,y;
	for(int i = 0;i<=2*n;i++){
		for(int j = 0; j<=(i<=n?i:n);j++){
			if(i == 0){
				dp[i][j] = 0;
				continue;
			}
			if(j == 0){
				dp[i][j] = dp[i-1][j] - a[i];
				continue;
			}
			x = dp[i-1][j-1] + (((1-a[i])==1)?0:(1000-a[i]));
			y = dp[i-1][j]- a[i];
			x = x<0.0?-x:x;
			y = y<0.0?-y:y;
			if(x<y || i == j)
			dp[i][j] = dp[i-1][j-1] + (((1-a[i])==1)?0:(1000-a[i]));
			else
			dp[i][j] = dp[i-1][j]- a[i];
		}
	}
	if(dp[2*n][n] <0)
	dp[2*n][n] = -dp[2*n][n];
	float ans = dp[2*n][n];
	ans /= 1000.00;
	cout << fixed;
	cout << setprecision(3) << ans << endl;
	
	return 0;
}