#include<stdio.h>
#define infile "fact.in"
#define outfile "fact.out"

long n;

void read()
{
	scanf("%ld",&n);
}
long f(long n)
{
	long rez=0,x=1;
	while(x<=n)
	{
		x=x*5;
		rez+=n/x;
	}
	return rez;
}
void solve()
{
	long a=1,b=5*n,m,x=0,q;
	while(a<=b && x==0)
	{
		m=(a+b)/2;
		q=f(m);
		if(q==n)
			x=m;
		if(q<n)
			a=m+1;
		if(q>n)
			b=m-1;
	}
	if(x==0)
		x=a;
	while(x%5!=0)
		x--;
	printf("%ld",x);
}
int main()
{
	freopen(infile,"r",stdin);
	freopen(outfile,"w",stdout);
	read();
	solve();
	fclose(stdin);
	fclose(stdout);
	return 0;
}