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#include <fstream>

using namespace std;
ifstream cin("fact.in");
ofstream cout("fact.out");
long long fact(long long i)
{
    long long suma=0,r=5;
    while(i/r)
    {
        suma=suma+i/r;
        r=r*5;
    }
    return suma;
}
int main()
{
    long long st=1,dr=900000000;
    long long p,poz=-23;
    cin>>p;
    while(st<=dr)
    {
        long long mij=st+(dr-st)/2;
        long long r=fact(mij);
        if(r==p)
        {
            poz=mij;
            dr=mij-1;
        }
        else
           if(p<r)
           {
               dr=mij-1;
           }
           else
             st=mij+1;
    }
    if(poz==-23)
       cout<<-1;
       else
   cout<<poz;
    return 0;
}