#include <iostream>
#include <fstream>
#include <limits.h>
using namespace std;
ifstream f("fact.in");
ofstream g("fact.out");

long start, stop, mij, p, raspuns=0;

int nr_zerouri(long k) {
	int a=0,b=5;
	while(k>=b) {
		a+=k/b;
		b*=5;
	}
	return a;
}

int cautare() {
	start=0;
	stop=5*p;
	mij=start+(stop-start)/2;
	
	while(start<stop) {
		mij=start+(stop-start)/2;
		cout<<nr_zerouri(mij)<<"\n";
		
		if(nr_zerouri(mij)==p) { return mij; }
		
		if(nr_zerouri(mij)>p) { stop=mij-1; }
		if(nr_zerouri(mij)<p) { start=mij+1; }
	    
		

	}
	return -1;
}
	

	
	
	
	
	

int main() {
	
	f>>p;

	cout<<cautare();
	
	
	
	f.close();
	g.close();
	return 0;
}