/*
 * Main.c
 *
 *  Created on: 18.09.2010
 *      Author: bugkiller
 */
#include <iostream>
#include <fstream>
using namespace std;
/**
 * Numarul de zerouri pentru n!
 */
int numara ( int n ){
	int old = n;
	int ret = 0;
	while ( n>0){
		ret+=n/5;
		n=n/5;
	}
	//cout <<"Numara" <<old <<" " <<ret << endl;
	return ret;
}

int main()
{
	int a;

	ifstream input ("fact.in");
	ofstream f ("fact.out");
	input >> a;
	//cin >> a;
    int left = 0;
    int right = 1<<31-1;
    int pos=-1;
    //cout << right;
    while ( left!=right){
    	//cout << left << " " << right << endl;
    	int m = (left+right)/2;
    	int rez = numara(m);
    	if ( rez==a ) {
    		pos = m;
    		break;
    	} else{
    		if ( rez>a){
    			// cautam in stanga
    			right=m-1;
    		} else{
    			// cautam in dreapta :)
    			left = m+1;
    		}
    	}
    }
    while ( pos>=1 &&  numara(pos-1)==a){
    	pos--;
    }
    //cout << pos;

    f << pos<< endl;

    input.close();
    f.flush();
    f.close();
    return 0;
}