#include<stdio.h>
long p;
long long unsigned i,sol;
int fact(int a)
{
	long s=0;
	while(a>1)
		{a=a/5;
 		 s=s+a;
      }
 return s;
 }
void solve()
{
	scanf("%ld",&p);
   for(i=0;i<=-1;i=i+5) if(fact(i)>=p){sol=i;break;}
   if (sol==0) printf("1");
   else printf("%ld",sol);
}
int main()
{
  freopen("fact.in","r",stdin);
  freopen("fact.out","w",stdout);
  solve();
  return 0;
}