#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;
    while(n!=0)
    {
        x++;
        if(x%25==0)
            n=n-pow(2,x/25);
        else if(x%5==0 || x%10==0)
            n--;
    }
    fout<<x;
}