#include <fstream>
#define nmax 500000

using namespace std;

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

int p, answer;

int nr_zero(int x)
{
    int s=0;
    s=x/5;
    return s;
}

int caut_binar()
{
    int left=0; int right=nmax, m;
    while(1)
    {
        m=(left+right)/2;
        if(nr_zero(m)>p) right=m-1;
        else if(nr_zero(m)<p) left=m+1;
            else break;
    }
    return m;
}

int main()
{
    f>>p;
    answer=caut_binar();
    g<<answer;
    return 0;
}