#include<fstream>
using namespace std;
#define DIM 1000000

int main(){
	ifstream fin ("fact.in");
	ofstream fout ("fact.out");
	int N,i=0,V[DIM],nr,j=0;
        fin>>N;
	while(i<=N){
		nr=5*i;
		while(nr%5==0)
			j++,nr/=5;
                i++;
	}
	if(i==N)
		fout<<5*(i-1)<<"\n";
	else
		fout<<-1<<"\n";
	fin.close();
        fout.close();
	return 0;
}