#include <iostream>
#include <fstream>
#include <cmath>
using namespace std;
ifstream fin("fact.in");
ofstream fout("fact.out");
int main()
{
    long long int n,p,x=0;
    fin>>n;
    if(n==0)
        fout<<1;
    else
    {
        while(n!=0)
        {
            x=x+5;
            if(x%25==0)
                n=n-pow(2,x/25);
            else if(x%5==0 || x%10==0)
                n--;
        }
        fout<<x;
    }
}