#include<fstream>
using namespace std;
ifstream cin("fact.in");
ofstream cout("fact.out");
int p,n;
int nr0(int x)
{
    int c=0,k=5;
    while (k<=x)
    {
        c+=x/k;
        k*=5;
    }
    return c;
}
int CautBin(int l,int r)
{
    if (l>r) return -1;
    int m=(l+r)/2, x=nr0(m);
    if (x==p) return m;
    if (x>p) return CautBin(l,m-1);
       else return CautBin(m+1,r);
}
int main()
{
    cin>>p;
    int c=CautBin(1,2000000000);
    while (c%5) c--;
    cout<<c;
    return 0;
}