#include<iostream.h>
#include<fstream.h>
#include<math.h>
int main ()
{
ifstream x("fact.in");
ofstream q("fact.out");
unsigned long a=0,b=32000;
unsigned int ok=0,z,p,i;
double kmax,c,n;
x>>p;
do
{
ok=1;
c=(a+b)/2; z=0;
kmax=log10(c)/log10(5);
for(i=1;i<=kmax;i++)
{
z=z+(n/pow(5,i));
}
if(z==p)
{
n=c;
ok=1;
q<<n;
}
else
{
if(z<p)
{
a=c+1;
}
else
{
b=c-1;
}}
}
while(ok!=1);
if(ok==0)
{
q<<-1;
}
x.close();
q.close();
return 0;
}