#include<stdio.h>
long long k,p;

long long nrz( long long k )
{
     long long p = 0;
     while( k )
     {
	    p += k/5;
	    k /= 5;
     }
     return p;
}

long long binary()
{
	long long a=0,b=10000000000,c;
	do
	{	c=(a+b)/2;
		if(nrz(c)==k)	break;
		else
			if(nrz(c)<k)	a=c+1;
			else		b=c-1;
	}
	while(a<b);
	printf("%lld",c-(c%5));
	return 0;
}

int main()
{
	freopen("fact.in","r",stdin) ;
	freopen("fact.out","w",stdout) ;
	scanf("%lld",&k);
	binary();

	return 0;
}