A. Natasha and Cats
time limit per test
1 second
memory limit per test
256 megabytes
input
standard input
output
standard output

Natasha has several cats at home. It is known that during the night, one cat drops from $$$A$$$ to $$$B$$$ poorly secured items (Natasha has an infinite number of such items).

One night Natasha heard in her sleep something fall $$$N$$$ times. Determine the minimum number of cats she could have.

Input

Three integers $$$A$$$, $$$B$$$, and $$$N$$$, each on a separate line.

Constraints: $$$0 \le A, B, N \le 10^9$$$, $$$A \le B$$$.

Output

Output a single non-negative integer — the minimum number of cats Natasha has. If there is no solution, output -1.

Examples
Input
2
3
5
Output
2
Input
2
2
3
Output
-1