var
        n,p,k,i,x:longint;
procedure citire;
var f:text;
begin
        assign(f,'factorial.in');
        reset(f);
        read(f,p);
        close(f);
end;

procedure determinare;
begin
        n:=1;
        repeat
                x:=0;
                if n=1 then
                begin
                        k:=0;
                        x:=0;
                end;
                k:=1;
                if n<>1 then
                begin
                        for i:=1 to n do
                                k:=k*i;
                        while k mod 10=0 do
                        begin
                                k:=k div 10;
                                inc(x);
                        end;
                end;
                inc(n);
        until x=p;
end;

procedure afisare;
var g:text;
begin
        assign(g,'factorial.out');
        rewrite(g);
        write(g,n-1);
        close(g);
end;

begin
        citire;
        determinare;
        afisare;
end.