#include <iostream>
#include <fstream>

using namespace std;
ifstream fin("fact.in");
ofstream fout("fact.out");
long long p, i, c, nr;

/// 5 10 15 20 25 30 35 40 45 50

int main()
{
    fin >> p;
    c = p;
    if(p == 0)
        fout << 1;
    else
    {
        for(i = 0; c > 0; c--, i += 5)
        {
            if(p - c == 5)
                nr++, p = c, c -= nr;
        }
        fout << i;
    }
    return 0;
}