[color=darkblue]Weightlifter Ruslan has just finished the exercise with a weight, which has $ n$ small weights on one side and $ n$ on the another. At each stage he takes some weights from one of the sides, such that at any moment the difference of the numbers of weights on the sides does not exceed $ k$. What is the minimal number of stages (in function if $ n$ and $ k$), which Ruslan need to take off all weights..[/color]
To determine the minimal number of stages required for Ruslan to take off all weights while ensuring that the difference in the number of weights on each side does not exceed \( k \), we can follow these steps:

1. **Initial Setup**:
   - Ruslan has \( n \) small weights on each side.
   - At each stage, he can take off up to \( k \) weights from one side.

2. **Strategy**:
   - To minimize the number of stages, Ruslan should take off the maximum number of weights (\( k \)) from one side, then from the other side, and continue alternating.

3. **Calculation**:
   - In each pair of stages (one from each side), Ruslan removes \( 2k \) weights in total.
   - The number of such pairs of stages required to remove most of the weights is given by \( \left\lfloor \frac{n}{k} \right\rfloor \).
   - After removing \( k \) weights from each side in \( \left\lfloor \frac{n}{k} \right\rfloor \) pairs of stages, the remaining weights on each side will be \( n \mod k \).

4. **Final Stages**:
   - If \( n \mod k \neq 0 \), there will be some remaining weights on each side. These remaining weights will require one additional stage for each side to be removed.
   - Therefore, the total number of stages required is \( 2 \left\lfloor \frac{n}{k} \right\rfloor + 2 \) if there are remaining weights.

5. **Edge Case**:
   - If \( n \mod k = 0 \), then no additional stages are needed after the pairs of stages. Thus, the total number of stages is \( 2 \left\lfloor \frac{n}{k} \right\rfloor \).

Combining these observations, the minimal number of stages required is given by:
\[ 2 \left\lfloor \frac{n}{k} \right\rfloor + 2 \]

The final answer is \( \boxed{ 2 \left\lfloor \frac{n}{k} \right\rfloor + 2 } \)