# include <fstream>
using namespace std;
ifstream fin ("fact.in");
ofstream fout("fact.out");
int zero(int n)
{
    int cnt = 0,p=5;
    while(n>=p)
    {
        cnt+=n/p;
        p*=5;
    }
    return cnt;
}
int main()
{
    int n,poz=-1;
    int st=1,dr=500000000;
    fin>>n;
    while(st<=dr)
    {
        int mij=(st+dr)/2;
        if(zero(mij)==n)
        {
            poz=mij;
            dr=mij-1;
        }
        else
            if(zero(mij)>n)
                dr=mij-1;
        else
            st=mij+1;
    }
    fout<<poz;
    return 0;
}