#include <iostream>
#include <fstream>

#define infile "fact.in"
#define outfile "fact.out"

using namespace std;

ifstream in(infile);
ofstream out(outfile);

int p;
int n;

int div5(int x)
{
    int r;
    for(r=0; x%5==0; x/=5){
        r++;
    }
    return r;
}

int main()
{
    in >> p;

    int nr5 = 0;
    for(n=1; nr5 < p; n++){
        nr5 += div5(n);
    }

    out << n-1;

    return 0;
}