#include <fstream>
#include <iostream>
using namespace std;
ifstream in("fact.in");
ofstream out("fact.out");
int main()
{
unsigned cs,s,n=0,nr,p,r=1,k=0,i=0;
in>>p;
s=0;
while (s!=p) {
    i++;
    if (i==5){
        i=0;
        k++;
        if (k%5==0)
            r++;
        s=s+r;
    }
    n=n+5;
    s=s+1;
}
if (s==0)
    n++;
out<<n;
    return 0;
}