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program main;
type
Row = Array[0..20] of Int64;
Grid = Array[0..20] of Row;
var
gridpath: Grid;
procedure init_grid();
var
i, j: Integer;
begin
for i := 0 to 20 do
begin
for j := 0 to 20 do
gridpath[i][j] := -1;
end;
end;
procedure calc(row: Integer; col: Integer);
var
r, c: Integer;
ret: Int64;
begin
ret := 0;
if gridpath[row][col] <> -1 then
exit;
r := row + 1;
c := col;
if (r <= 20) and (c <= 20) then
begin
calc(r, c);
ret := ret + gridpath[r][c];
end;
r := row;
c := col + 1;
if (r <= 20) and (c <= 20) then
begin
calc(r, c);
ret := ret + gridpath[r][c];
end;
gridpath[row][col] := ret;
end;
begin
init_grid();
gridpath[20][20] := 1;
calc(0, 0);
writeLn(gridpath[0][0]);
end.
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