#include <bits/stdc++.h>
using namespace std;

ifstream in("fact.in");
ofstream out("fact.out");

int factorial(int nr){
    vector<int> zeros;

    for (int i = 2; i <= nr; i++){
        if (i % 2 == 0 || i % 5 == 0)
            zeros.push_back(i);
    }

    int final = 1;


    for (int item : zeros)
        final *= item;

    int nr_of_zeros = 0;
    
    while(final){
        if(final % 10 != 0)
            break;
        nr_of_zeros++;
        final /= 10;
    }

    return nr_of_zeros;
}

int main(){
    int n, fact;

    in >> n;

    if (n == 0){
        out << 1 << "\n";
        return 0;
    }

    if (n == 1){
        out << "10\n";
        return 0;
    }

    /*for(int i = 2; ;i++)
        if (n == factorial(i)){
            out << i << "\n";  
            return 0;
        }
    */

    int temp = n * 5;
    if (factorial(temp) == n){
        out << temp << "\n";
    } else {
        out << temp - 5 << "\n";
    }

    return 0;
}