#include <iostream>
#include <algorithm>
#include <vector>
#include <string>
#include <math.h>
#include <map>
#include <stdlib.h>
#include <sstream>
#include <stdio.h>
using namespace std;
#define PI 3.1415926535897932384626433832795

#define MAX 1001

int main() {
    freopen("fact.in", "r", stdin);
    freopen("fact.out", "w", stdout);

    long long n, p, sum, aux;

    scanf("%I64d", &p);
    if (p == 0) {
        cout << "1";
        return 0;
    }
    for (n = 4*p / 5;; n++ ) {
        sum = 0;
        aux = n / 5;
        while(aux) {
            sum += aux;
            aux /= 5;
        }
        
        if (sum == p) {
            printf("%I64d", n);
            return 0;
        }
    }

    return 0;
}