#include<stdio.h>
long long n,p,st=1,dr,bla,t,nr;
int main()
{
	freopen("fact.in","r",stdin);
	freopen("fact.out","w",stdout);
	scanf("%ld",&p);
	dr=5*p;
	while(st<=dr)
	{
		nr=0;
		t=(st+dr)/2;
		bla=5;
		while(bla<=t)
		{
			nr=nr+t/bla;
			bla=bla*5;
		}
		if(nr>=p)
			dr=t-1;
		else
			st=t+1;
	}
	if(p==0)
		printf("1");
	else
		printf("%ld",t);
}