Lagrang Metod for two variable function

CLS:BEEP:SCREEN 0,0,0:COLOR 9,0
INPUT N :IF N<1 THEN 20
DIM X(N), Y(N), F(N,N), L(N), M(N), K(N,N)
FOR I=0 TO N :READ X(I), Y(I) :NEXT I
PRINT
DATA 0,0,.524,.524,1,1
FOR I=0 TO N
FOR J=0 TO N
READ F(I,J) :PRINT F(I,J)
NEXT J
PRINT
NEXT I
DATA 1,1,1,1.689,1.626,1.462,2.718,2.353,1.469
PRINT "---------------------------------------"
INPUT "x,y=?",X,Y
PRINT "---------------------------------------"
FOR I=0 TO N
L(I)=1
FOR J=0 TO N
IF I=J THEN 220
L(I)=L(I)*(X-X(J))/(X(I)-X(J))
NEXT J
NEXT I
FOR I=0 TO N
M(I)=1
FOR J=0 TO N
IF I=J THEN 290
M(I)=M(I)*(Y-Y(J))/(Y(I)-Y(J))
NEXT J
NEXT I
FOR I=0 TO N
FOR J=0 TO N
K(I,J)=L(I)*M(J)
PRINT K(I,J);
NEXT J
PRINT
NEXT I
PRINT "---------------------------------------"
FOR I=0 TO N
FOR J=0 TO N
F(I,J)=F(I,J)*K(I,J)
PRINT F(I,J);
S=S+F(I,J)
NEXT I
NEXT J
PRINT
PRINT "f(";X;",";Y;")";S