Program Factorial;

var p,n,x,k,r,m:longint;
    f:real;
    z:boolean;
    i,o:text;

begin
    assign(i,'fact.in');
    assign(o,'fact.out');
    reset(i);
    rewrite(o);
    Read(i,p);
    n:=1;f:=1; z:=true;k:=0;
    While (k<=100000000) and z do begin
                                       f:=f*n;
                                       inc(n);
                                       if (n mod 5=0) and (n div 5<>0) then begin
                                                                          x:=n;m:=1;
                                                                          While m<>x do begin
                                                                                         m:=m*5;
                                                                                         inc(r);
                                                                                         end;
                                                                          k:=k+r;
                                                                          end;
                                       if (k=p) then z:=false;

                     end;
    if  (k=p) and (k<=100000000) then Write(o,n)
                                else Write(o,-1);

    close(i);
    close(o);
end.