#include<fstream>

using namespace std;
ifstream fi("fact.in");
ofstream fo("fact.out");
int d,c;
int main()
{
int p;
fi>>p;
for(int i=1;i<=100000000;i++)
{if(i%2==0)
d++;
if(i%5==0)
    c++;
int h;
h=d;
if(c<d)
    h=c;
if(h==p)
{
    fo<<i;break;
}

}}