used:
...
for(i=1;i<=S;i++)
for(j=i;j<=S;j++)
...
But the result is 'Time limit exceeded'.  Please help, why 'Time limit exceeded'?

don't use brute force... O(n^2) n=30000 ===>>> time limit)

hint: you can don't use N in your solution

brute force (with some optimizations) works fine