第一题
#include<iostream>
#include<vector>
#include<algorithm>

using namespace std;

int main()
{
int n, icount = 1, temp = 1;
cin >> n;
if (n == 1)
{
cout << 3 - n;
return 0;
}
vector<int>data(n);
for (int i = 0; i < n; i++)
{
cin >> data[i];
}
sort(data.begin(), data.end());
for (int i = 0; i < n - 1; i++)
{
if (data[i + 1] - data[i]>20 || temp == 3)
{
icount++;
temp = 1;
}
else
{
temp++;
}
}
cout << icount * 3 - n;
return 0;
}