#include<iostream.h>
#include<fstream.h>
main()
{
long int s,t,p,x,a[15000],b[15000],i,j,k,l,m,n,sp,aux,valid;
fstream f("fact.in",ios::in);
fstream g("fact.out",ios::out);
f>>p;
m=1000000;l=5;
if(p==0)g<<"1";
if(p==1)g<<"2";
else
{
 k=2;valid=0;sp=0;
 do{
    if(k==l){sp++;l*=5;}
    if(p==k){x=5*k;valid=1;}
    k++;
    }while((valid!=1)&&(k<=m));
 }
sp*=5;
x-=sp;
g<<x;
f.close();
g.close();
return 0;
}