#include<fstream>
using namespace std;

int main(){
	long long p,nr,m=0,i;
	ifstream in;
	in.open("fact.in");
	in>>p;
	in.close();
	ofstream out("fact.out");
	for(i=1;1;i+=5){
		m=i;
		nr=0;
		while(m/5){
			m/=5;
			nr+=m;
			}
		if(nr==p){
			out<<i;
			break;
			}
		if(i==1)
			i--;
		}
	return 0;
	}