#include<fstream>
using namespace std;
 
long zero(long x)
   { long putere=1, z=0;
     while (putere<=x)
         { putere*=5;
           z+=x/putere; }
     return z; 
   };
 
int main () {
ifstream f1("fact.in");
ofstream f2("fact.out");
 
long p,st,dr,m;
f1>>p;
st=1; dr=5*p;
while (st<=dr)
{   
    m=(st+dr)/2;
    if (p<= zero(m))
        dr=m-1;
    else 
        st=m+1; 
}
if (zero(st)==p)
f2<<st;
else f2<<-1;
f1.close();
f2.close();
return 0; 
}