#include<fstream>
using namespace std;
int main()
{ int p,i,g,max=0;
ifstream in("fact.in");
ofstream out("fact.out");
in>>p;
if(p==0)
{out<<1<<endl;
}
else
{
for(i=1;p>=0;i++)
{g=i;
if(i>max)
{max=i;
}
while(g%5==0)
{g=g/5;
p=p-1;
}
}
if(max<125)
{
out<<max-5<<endl;
}
if(max>=125&&max<625)
{
	out<<max-10<<endl;
}
}
in.close();
out.close();
return 0;
}