#include<stdio.h>
#define LL long long
#define min(a,b) (a<b ? a : b)
LL p;
void read()
{
freopen("fact.in","r",stdin);
freopen("fact.out","w",stdout);
scanf("%lld",&p);
}

LL p2(LL n)
{
LL num=2,s=0;
while(n/num)
	{
	s+=n/num;
	num=num<<1;
	}
return s;
}

LL p5(LL n)
{
LL num=5,s=0;
while(n/num)
	{
	s+=n/num;
	num=num*5;
	}
return s;
}

LL okay(LL n)
{
return min(p2(n),p5(n));
}

void solve()
{
LL st=1,dr=(LL)1<<63,m,last=-1;
while(st<=dr)
	{
	m=(st+dr)>>1;
	if(okay(m)>=p)
	   {
	   dr=m-1;
	   if(okay(m)==p && (m<last || last==-1))
		last=m;
	   }
	else
	   st=m+1;
	}
printf("%lld\n",last);
}
int main()
{
read();
solve();
return 0;
}