#include<cstdio>
using namespace std;
long long unsigned int s,p,c,a,b,ok,aux;
void calcul(){
	s=0;
	while(c!=0){
		c/=5;
		s+=c;
	}
}
int main(){
	freopen("fact.in","r",stdin);
	freopen("fact.out","w",stdout);
	scanf("%lld%",&p);
	a=0;
	b=100000000;
	ok=0;
	aux=p;
	while(aux>1){
		aux/=5;
	}
	if(aux==1)
		printf("%d",-1);
	else{
	while(ok==0){
		c=(a+b)/2;
		s=0;
		aux=c;
		calcul();
		if(s==p)
			ok=1;
		else{
			c=aux;
			if(s<p)
				a=c+1;
			else
				b=c-1;
		}
	}
	printf("%lld",aux-(aux-aux/5*5));
	}
	return 0;
}