программка на PascalABC

var
s1, s2, sr: string;
p1, p2, c: integer;
begin
write('s1? ');
readln(s1);
write('s2? ');
readln(s2);
sr := '';
for c := 1 to length(s1) do
if (pos(s1[c], s1) = c) and (pos(s1[c], s2) <> 0) then
sr := sr + s1[c];
writeln('result: ', sr);
end.

ЗЫ: ХЗ работает или нет?

Ну как-то так:
var S1 : set of Char := []; var S2 : set of Char := []; for var N : Integer := 1 to Slovo1.Length do if Slovo1[N] in S1 then S2 := S2 + [Slovo1[N]] else S1 := S1 + [Slovo1[N]];
var S3 : set of Char := []; var S4 : set of Char := []; for var N : Integer := 1 to Slovo2.Length do if Slovo2[N] in S3 then S4 := S4 + [Slovo2[N]] else S3 := S3 + [Slovo2[N]];
S1 := S1 - S2;
S3 := S3 - S4;
var S0 : set of Char := S1 * S3;
var K : Integer := 0; for var C : Char := #0 to #255 do if C in S0 then Inc(K);
if K = 0 then begin WriteLn('Нет таких символов'); Exit; end;
Write('Слово: '); for var C : Char := #0 to #255 do Write(C); WriteLn;
Только это строго в Паскале АБЦ!