#include<stdio.h>
long nr,p;
long nz(long p)
{long nr=0;
 while(p%5==0) {nr++;  p=p/5;}
 return nr;}
long nrzero(long n,long nri,long p)
{long nr=nri;
 for(long i=p-p%5+5;i<=n;i=i+5)
  nr=nr+1+nz(i/5);
 return nr;}
long div(long inc,long sf,long nr)
{long m=(inc+sf)/2,nz,nrm;
 nz=nrzero(m,nr,inc);
 if(nz==p) return m;
 if(nz<p) return div(m,sf,nz);
 return div(inc,m,nr);
}
int main()
{freopen("fact.in","r",stdin);
 scanf("%ld",&p);
 fclose(stdin);
 if(p==0) nr=1;
 else nr=div(1,5*p,0);
 while(nr!=1&&nr%5) nr--;
 freopen("fact.out","w",stdout);
 printf("%ld",nr);
 fclose(stdout);
 return 0;}