#include<fstream>
using namespace std;
ifstream cin("fact.in");
ofstream cout("fact.out");
int n,k,p,rez;
int nrde_zerouri(int n){
	int u=0;
	for(int i=5;i<=n;i*=5)u=u+(n/i);
	return u;
}
int main(){
	cin>>n;
	int st=1;
	int dr=100000000;
	rez=-1;
	while(st<=dr){
		int pivot=(dr-st)/2+st;
		int o=nrde_zerouri(pivot);
		if(o==n){rez=pivot;dr=pivot-1;}
		else if(o>n)dr=pivot-1;
		else st=pivot+1;
	}
	cout<<rez;
}