let fee_bps = (-8_300_000_i64)
    .checked_mul(slots_passed as i64)
    .ok_or(ContractError::ArithmeticError)?
    .checked_add(2_162_600_000)
    .ok_or(ContractError::ArithmeticError)?
    .checked_div(100_000)
    .ok_or(ContractError::ArithmeticError)?;
let fee_bps = (-8_300_000_i64)
    .checked_mul(slots_passed as i64)
    .ok_or(ContractError::ArithmeticError)?
    .checked_add(2_162_600_000)
    .ok_or(ContractError::ArithmeticError)?;
let fee = amount
    .checked_mul((fee_bps as u64))
    .ok_or(ContractError::ArithmeticError)?
    .checked_div(1_000_000)
    .ok_or(ContractError::ArithmeticError)?;
