The Evil Professor

Do you know Professor Saeed? He is the algorithms professor at Damascus University. Yesterday, he gave his students hard homework (he is known for being so evil) - for a given binary string $S$, they should compute the sum of $F(S, L, R)$ over all pairs of integers $(L, R)$ ($1 \le L \le R \le |S|$), where the function $F(S, L, R)$ is defined as follows: - Create a string $U$: first, set $U = S$,