i'm think test 3 incorrect.

if use this method for read input data we got WA
scanf("%s1 %s2",s1,s2);
S1 = (s1[0]-'0')*1000 + (s1[1]-'0')*100 +(s1[2]-'0')*10 +(s1[3]-'0')*1;
S2 = (s2[0]-'0')*1000 + (s2[1]-'0')*100 +(s2[2]-'0')*10 +(s2[3]-'0')*1;

if use
scanf("%d %d",&S1,&S2);
we has CA