program kadai
implicit none
integer  ::  n,m
integer,allocatable  ::  a(:),b(:)
integer  ::  i,k,j
integer  ::  fir,las
integer  ::  ans,flag
integer  ::  loc

read(*,*) n,m
allocate(a(n))
allocate(b(n))

do i=1,n
    read(*,*) a(i),b(i)
end do


ans=0
call qsort(a,b)

j=1
fir=1
flag=0
las=1
do k=1,m
    do i=j,n
        if (a(i)==k) then
            flag=1
        end if
        if ((flag==1 .and. (a(i)>k .or. i==n))) then
            flag=0
            las=i-1
            if (i==n) then
                las=n
            end if
            exit
        end if
        if (a(i)>k) then
            flag=2
            exit
        end if
        j=j+1
    end do

    if (flag /= 2) then
        loc=maxloc(b(1:las),1)
        ans=ans+b(loc)
        b(loc)=0
    end if

end do

write(*,*) ans


stop

contains


subroutine swap(a,b)
implicit none
integer,intent(inout)  ::  a,b
integer  ::  c
c=a
a=b
b=c
end subroutine swap

subroutine qsort(x,y)
implicit none
integer, intent(inout)  ::  x(:)
integer, intent(inout)  ::  y(:)
integer  ::  first,last
first=1
last=size(x)
call q2sort(x,y,first,last)
return
end subroutine qsort

recursive subroutine q2sort(x,y,first,last)
implicit none
integer, intent(inout)  ::  x(:)
integer, intent(inout)  ::  y(:)
integer, intent(inout) ::  first,last
integer  ::  fir, las
integer  ::  i,j
integer  ::  n
    n=x((first+last)/2)
    i=first
    j=last
    do
        do while (x(i)<n)
            i=i+1
        end do
        do while(x(j)>n)
            j=j-1
        end do
        if (i>j .or. i==j) then
            exit
        end if
        call swap(x(i),x(j))
        call swap(y(i),y(j))
        i=i+1
        j=j-1
    end do
    if (first<i-1) then
        las=i-1
        call q2sort(x,y,first,las)
    end if
    if (last>j+1) then
        fir=j+1
        call q2sort(x,y,fir,last)
    end if
end subroutine q2sort

end program kadai
