#include<cstdio>
using namespace std;
long long int p,nr,nrn,pp;
int calcul(){
	nr=p;
	while(nr>1){
		nr/=5;
	}
	return nr;
}
int main(){
	freopen("fact.in","r",stdin);
	freopen("fact.out","w",stdout);
	scanf("%d",&p);
	if(calcul())
		printf("%d",-1);
	else{
		nrn=0;
		pp=5;
		while(pp<p){
			pp*=5;
			++nrn;
		}
	printf("%lld%",5*p-nrn*5);
	}
	return 0;
}