#include <fstream.h>
long int nr,p,aux,aux2,s;
ifstream f;ofstream g;
int main()
{f.open("fact.in");g.open("fact.out");
while(!f.eof())
{f>>p;f.get();
 nr=0;s=1; aux2=0;
 while(aux2!=p)
 { nr++;
 aux=nr;aux2=0;
    while(aux)
    {aux2+=(aux/5);
    aux/=5;
    }
  }
  if(nr==0)g<<"-1"<<'\n';
else
g<<nr<<'\n';
}

f.close();g.close();
return 0;
}