#include<fstream.h>
long p,r,n;
int main()
{ifstream f("fact.in");
ofstream g("fact.out");
f>>p;
n=p%5;
r=p/5;
if(n==0)
	r=r-1;
n=p*5-5*r;
g<<n;
f.close();
g.close();
return 0;
}