#include <fstream>

using namespace std;
ifstream fin("fact.in");
ofstream fout("fact.out");
int nr0(int x)
{
    int p=5, rez=0;
   while(p<x)
   {
       rez+=x/p;
       p*=5;
   }
   return rez;
}
int cb(int x)
{
    int dr=100000000, st=1, mid;
    while(st<dr)
    {
        mid=(dr+st+1)/2;
        if(nr0(mid)>x)
        {
            dr=mid-1;
        }
        else
            st=mid;
    }
    return st;

}
int main()
{
    int n;
    fin>>n;
    fout<<cb(n)-4;
    return 0;
}