#include <iostream>
#include <fstream>
using namespace std;
ifstream f("fact.in");
ofstream g("fact.out");
int n,p,i,x,zero;
int main()
{
    n=1;
    f>>p;
    for (i=1; ;i++)
    {
        n*=i;
        x=n;
        zero=0;
        while (x)
        {
            if (x%10==0) zero++;
            else break;
            x/=10;
        }
        if (zero==p) {g<<i; return 0;}
    }
    //cout << "Hello world!" << endl;
    return 0;
}